Symmetrix Remote Data Facility (SRDF) Product Description ... - EMC

Symmetrix Remote Data Facility 

Product Description Guide Enterprise Storage Software

SYMMETRIX REMOTE DATA FACILITY PRODUCT DESCRIPTION GUIDE 

Symmetrix Remote Data Facility (SRDF) 

Product Description Guide 

Table of Contents 3 Chapter 1: Introduction 

3 Overview 

3 The Value of Symmetrix Remote Data Facility 

4 Business Impact 

4 Operational Impact 

5 Financial Impact 

5 EMC’s Architectures for Enterprise Storage: ISA and MOSAIC:2000 

6 Information Protection 

7 Information Sharing 

7 Information Management 

8 SRDF and Symmetrix 

9 SRDF and Fibre Channel 

9 SRDF and IP 

10 SRDF and EMC TimeFinder 

10 SRDF and AS/400 Environments 

11 Chapter 2: SRDF Uses and Applications 

11 Overview 

11 Disaster Recovery, the Old Way 

11 Disaster Scenarios 

12 Disaster Recovery Sites 

12 Traditional Techniques for Data Recovery 

12 Store the Tape Copies at a Secure Site 

13 Create the Tape Copies at the Recovery Site 

13 Data Copies on Disk 

13 Using the Host/Server to Create the Copies 

13 Disaster Recovery Testing 

13 Business Continuity 

14 Eliminating the “Race to Sunrise” 

14 Loading Data Warehouses 

14 Scheduled Maintenance 

14 Data Center Migrations 

14 Workload Migrations 

14 AS/400 Applications 

16 Growing Your Business with SRDF 

16 SRDF Over IP Optimizes Information Deployment 

16 SRDF Over Fibre Channel Increases Throughput 

17 Chapter 3: SRDF Detailed Description 

17 SRDF Principles of Operation 

17 SRDF Hardware Components 

19 SRDF Implementation 

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20 Installation and Planning 

20 Supported Environments 

21 Multihost Support 

22 SRDF Campus Solution 

23 SRDF Extended Distance Solutions 

23 SRDF FarPoint 

23 SRDF Multi-hop Capability 

24 SRDF over IP for Extended Distances 

24 SRDF Modes of Operation 

24 Synchronous Mode 

25 Semi-Synchronous Mode 

26 Adaptive Copy Mode 

26 Consistency Group Utility 

27 Domino Option 

27 SRDF FarPoint Option 

27 Invalid Tracks Attribute 

27 SRDF Management 

28 Chapter 4: SRDF Usability Considerations 

28 SRDF Features and Capabilities 

28 Sequential Data Updates Across the Link 

28 Local and Remote Mirrors of the Same Volume 

28 SRDF and RAID-S Compatibility 

28 Dynamic Sparing 

28 Source/Target Switching 

29 Source Control of Target 

29 HP MetroCluster 

30 Potential Events 

30 Local or Remote Volumes 

30 Link Breaks 

30 Return to Source Site 

31 Synchronization and Resynchronization 

31 Use of Track Tables 

32 Performance 

32 Data Recovery 

32 Databases 

33 Backup Using Remote Data 

33 Read-Only Access to Target Volumes 

33 SRDF Testing 

34 Chapter 5: Symmetrix Software Solutions and Service 

34 Software Solutions 

35 Professional Services 

35 Enterprise Business Continuity 

36 Enterprise Storage Architecture and Design ñ Building an E-Infostructure 

36 Enterprise Storage Network 

36 Support and Service 

2 


Chapter 1 

Introduction 

Overview This guide describes Symmetrix Remote Data Facility, SRDF , EMC’s industry-leading 

information protection and business continuity software solution for use with Symmetrix ® 

enterprise storage systems. 

Chapter 1 provides an overview of SRDF, its capabilities, and its benefits for today s informationcentric 

enterprises. The chapter also includes a general discussion of Symmetrix, EMC’s intelligent 

enterprise storage system, the Symmetrix architecture, and EMC’s other information protection, 

information sharing, and information management solutions. The remaining chapters provide a 

greater level of detail and operational description on the material presented in Chapter 1. 

The Value of Symmetrix EMC Enterprise Storage helps you realize your most aggressive business goals through 

Remote Data Facility intelligent information sharing, management, and protection. Achieving those goals is what we 

call experiencing The EMC Effect . Symmetrix Remote Data Facility helps you achieve The EMC 

Effect by providing you with complete business continuity that can accelerate your business in the 

new E-based economy. With SRDF the data center is secure from both unforeseen disasters and 

planned events such as daily backups, database loads and refreshes, application testing, scheduled 

maintenance, and data center migrations or consolidations. Equally important, EMC has 

expanded SRDF’s capabilities to include Virtual Private Networks using the Internet Protocol (IP), 

and Fibre Channel technology. 

SRDF is the only solution providing automatic information protection/business continuity 

simultaneously to mainframe, UNIX ® , Windows NT ® , and AS/400 ® systems. SRDF offers a 

host-independent, mirrored data storage solution that duplicates production or source site data on 

a physically separate recovery or target site transparently to users, applications, databases, and 

host processors. 

When primary (that is, source) stored data is unavailable, SRDF enables fast switchover to the 

target copy data so that critical information is again available in minutes. Business operations and 

related applications resume full functionality with minimal interruption. Source and target site 

Symmetrix systems can be adjacent to one another or thousands of miles apart. In either case, the 

same enterprise-level information protection capabilities are afforded. After such an event, SRDF 

can resynchronize data to the source or to the target, at the users’ discretion, thereby ensuring 

information and database consistency. 

3 

SYMMETRIX A SYMMETRIX B

Business Impact SRDF’s unique capabilities enable: 


Without SRDF, planned or unplanned events can disrupt data center operations and prevent access 

to vital business data. Business, operational, and financial losses can be significant. SRDF helps 

protect against these losses and their impact on your enterprise. Besides offering data protection, 

SRDF over IP capitalizes on e-focused business trends, while Fibre Channel connectivity offers 

high-speed, efficient and effective data transfers in local or campus configurations. Using SRDF 

dramatically impacts any organization’s business, operations, and finances. 

• • • 1 Business Impact 2 Operational Impact 3 Financial Impact 

• Enhanced customer service due to reduced planned and unplanned downtime. 

• Faster recovery from planned and unplanned downtime, increasing the availability of revenuegenerating 

applications. 

• Deployment of underutilized IP networking structure for low cost information access to local and 

remote sites. 

• Support for Fibre Channel architecture, thus expanding connectivity options for open systems and 

Symmetrix to Symmetrix data mirroring. 

• Longer running of transactional applications, resulting in increased revenue. 

• Additional business applications and opportunities gained from higher data availability. 

• Incremental uses of remotely mirrored data. 

Operational Impact SRDF improves enterprise processes by streamlining operations, enhancing efficiency, and 

protecting business assets. SRDF enables: 

• Improved disaster recovery procedures through the elimination of slow, labor-intensive tape-based 

retrieval and loading schemes. 

• Increased throughput for business-critical information with high-speed Fibre Channel 

• Ability to deploy remote copies of files and databases to previously inaccessible sites using 

IP networks. 

• More frequent and less costly online testing of disaster recovery scenarios, providing confidence in 

a viable and flexible solution. 

• Simultaneous support of heterogeneous mainframe, UNIX, Windows NT, and AS/400 systems, 

reducing complexity and simplifying IS staff training requirements. 

• Database integrity consistently maintained and preserved through built-in synchronization 

functionality. 

• No special coding or software applications required, simplifying its use. 

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Financial Impact Direct impact on the revenue-generating and service-providing aspects of SRDF includes: 

• Elimination of expensive and inflexible manual backup and restore procedures. 

• Improved cost-effectiveness through direct Symmetrix-to-Symmetrix operation — CPU 

redundancy is unnecessary and performance is enhanced. 

• Savings in telecommunication costs using SRDF over IP networks. 

• High throughput and connectivity characteristics of Fibre Channel improving local and campus 

data protection and replication. 

• Cost-effective resource utilization ó a single SRDF target site can support multiple source sites, 

each with multiple hosts. 

• Immediate return on SRDF investment justified by preventing just one extended outage. 

EMC’s Architectures EMC Enterprise Storage systems and solutions are built on the foundation of Intelligent Storage 

for Enterprise Storage: Architecture (ISA) and MOSAIC:2000 ® — a combination of industry-standard software and 

ISA and MOSAIC:2000 hardware — to achieve unsurpassed levels of information protection, information sharing, and 

information management. EMC’s Enterprise Storage architecture ensures optimum performance, 

availability, scalability, and connectivity. Complementary ISA software and MOSAIC:2000 

hardware architectures demonstrate the unique storage system philosophy of all EMC Enterprise 

Storage products working together to solve our customers’ biggest IT challenges. 

An EMC Enterprise Storage system: 

• Stores and retrieves data from all major computing platforms, including mainframe and open 

systems environments. 

• Enables software-based functionality that ensures business continuity even in the event of a disaster. 

• Delivers rapid and non-disruptive data migration from one system to another. 

• Shares information, regardless of origin. 

EMC’s Intelligent Storage Architecture, ISA, consolidates information sharing, management, and 

protection into a single intelligent storage system capable of managing the information storage and 

retrieval needs of the entire enterprise. 

5 

Database Applications Management 

SRDF 

storage activity easy. 

Information Management 

Provides graphical user 

interfaces to make configuration 

and management of 

Performance, 

Availability 

APIs 

Connectivity 

Information Protection 

Ensuring the highest availability 

in the event of planned or 

unplanned information systems 

interruptions. 

MOSAIC:2000 

Information Sharing 

Multihost support allows 

high-speed movement of large 

amounts of information between 

different platforms. 

Maintainability, 

Scalability, Compatibility


MOSAIC:2000 combines industry-standard hardware with optimized software to provide the 

highest performance, availability, scalability, and performance. 

EMC’s architectural approach lets you easily integrate the enhancements that advances in software 

and hardware technology offer. The basic system infrastructure remains constant when you add or 

replace elements. This adaptability allows EMC Enterprise Storage to remain on the leading 

edge of user needs and technology improvements while preserving existing information 

technology investments. 

Information Protection In addition to Symmetrix Remote Data Facility, EMC also provides a variety of other hardware 

and software information protection features. These include extensive RAID (Redundant Array of 

Independent Disks) data protection, Mirroring (the optimum RAID level for both performance 

and availability), EMC’s RAID-S enhanced parity protection, and Dynamic Sparing. EMC 

Symmetrix also affords automatic ‘phone home’ diagnostic capabilities so that failing parts can be 

replaced before they become troublesome. 

Other integrated and optional EMC information protection software and service offerings include 

the following: 

• SRDF FarPoint , an advanced SRDF capability, significantly increases SRDF performance over 

extended distances through the optimization of the communication line. 

• EMC TimeFinder provides the optional capability for system administrators to create, in 

background mode, independently addressable Business Continuance Volumes (BCVs) that can be 

used to run other tasks simultaneously with normal production activities. This capability is known 

as “workload compression.” 

• EMC Foundation Suite by Veritas and EMC Database Edition for Oracle by Veritas. Both of these 

suite products are tightly integrated with EMC TimeFinder, providing parallel BCV operations to 

Veritas File System and Volume Manager users. 

• Symmetrix Data Migration Services (SDMS ) is an optional EMC service that enables users to 

migrate large or small volumes of data off heterogeneous mainframe storage devices or other 

Symmetrix systems to new Symmetrix systems without stopping business operations during 

the migration. 

• EMC CopyPoint is optional software that works with SRDF to extend SRDF capabilities in 

AS/400 environments. 

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• EMC CopyCross is optional mainframe-based software that intercepts data originally targeted for 

tape systems and redirects it onto Symmetrix. Once on Symmetrix it can be SRDF’s to a remote 

Symmetrix for disaster recovery purposes. The result is a fast post-disaster restart for tape-based 

data — as fast as any other disk-based data. Customers avoid waiting for the arrival of physical 

computer tapes. Instead, they work with Symmetrix disk images of the same information. 

Information Sharing EMC Enterprise Storage systems provide a centralized, shareable information repository in 

support of changing environments and mission-critical applications. This leading-edge technology 

begins with physical devices shared between heterogeneous operating environments and extends to 

specialized software that enhances information sharing between disparate platforms. 

• Symmetrix provides standard simultaneous multiple system support 

• EMC Enginuity Operating Environment makes it possible for Symmetrix systems to serve as the 

foundation for a scalable, open and manageable information storage infrastructure 

• Symmetrix Enterprise Storage Platform (ESP) software provides simultaneous mainframe and 

open systems support for Symmetrix storage systems 

• EMC Celerra is unique hardware and software that brings unprecedented levels of availability, 

management, and scalability to network file storage 

• EMC InfoMover , formerly known as Symmetrix Multihost Transfer Facility (SMTF), facilitates 

high speed bulk file transfers between heterogeneous host platforms without the need for 

network resources 

• Application Programming Interfaces (APIs) enable customers and third-party vendors to tightly 

integrate their software solutions with hardware and software from EMC 

Information Management EMC Enterprise Storage systems improve information management by allowing users to 

consolidate storage capacity for multiple hosts and servers. EMC offers powerful graphical user 

interface (GUI)-based tools that dramatically simplify and enhance Symmetrix monitoring 

and control. 

• EMC Data Manager (EDM ), a combined hardware and software system, supports open system 

backup needs from one centrally managed site while offering a complete, high-performance 

database backup solution for the entire enterprise. 

• EMC PowerPath offers a combination of simultaneous multiple path access, workload balancing, 

and path failover capabilities between Symmetrix systems and supported server hosts. 

• EMC ControlCenter provides extensive user control, performance monitoring of data in real time, 

error condition identification, and configuration management of Symmetrix systems in mainframe 

and open system environments. 

7


The GUI screens of EMC ControlCenter provide easy point-and-click monitoring and control of 

SRDF environments, as well as planning, monitoring, and managing other EMC hardware and 

software functions plus those from third parties which are compliant. 

SRDF and Symmetrix The unique capabilities of SRDF enhance the already impressive information protection and 

availability capabilities of EMC’s Symmetrix enterprise storage system. Standard Symmetrix 

protection features include: 

• Full-system battery backup 

• Redundant disk and channel directors 

• A choice of RAID protection levels 

— Mirroring, EMC’s RAID 1 protection 

— RAID-S, EMC’s enhanced parity-based protection 

• Fully non-disruptive microcode loads 

• Non-disruptive component replacement 

• Dynamic disk sparing 

• Automatic cache and disk scrubbing 

• Integrated Remote Maintenance Processor (RMP) with automatic “phone home” capability 

8 


SRDF adds business continuity protection to Symmetrix’s standard information protection 

features. All SRDF protection features are available for Symmetrix systems whether in support of 

mainframe, open systems, or heterogeneous environments. 

SRDF extends business continuity protection by providing separate copies of data on physically 

separate Symmetrix systems. If data becomes unavailable on one Symmetrix, it can be accessed by 

the other Symmetrix system(s). 

SRDF and Fibre Channel For sites requiring a higher level of throughput and real-time mirroring, EMC offers SRDF within 

the Fibre Channel (FC) architecture. Fibre Channel increases SRDF throughput significantly. Fibre 

Channel affords major benefits to enterprise storage in terms of consolidation, distance between 

Symmetrix SRDF sites, connectivity, and performance. Together, SRDF and Fibre Channel boost 

the throughput performance of existing technologies as well as provide great flexibility for 

open systems. 

EMC offers a fully integrated, highly available Fibre Channel-based Enterprise Storage Network 

(ESN) system called the EMC Connectrix system. The single enclosure Connectrix system houses 

either one or two Fibre Channel directors supporting up to 64 Fibre Channel ports, a service 

processor, connectivity management application software, and an efficient cable management 

system. The highly modular and scalable system offers an array of configuration choices for a 

variety of connectivity and availability requirements. ESN provides significant advantages in terms 

of information consolidation, connectivity, multi-host support, and ease of management. Using 

SRDF in combination with Connectrix means that SRDF Symmetrix to Symmetrix transfers as 

well as host to Symmetrix transfers occur through an Enterprise Storage Network (ESN) using 

Fibre Channel protocol. SRDF, Connectrix, and Fibre Channel technologies provide a capable 

foundation for your storage architecture while serving as the basis for future business and 

technology expansion. 

SRDF and IP SRDF now enables the automatic replication of data and applications between geographically 

separated EMC Symmetrix Enterprise Storage Systems over Virtual Private Networks using the 

Internet Protocol (IP). This unique feature takes advantage of the ubiquitous and often 

underutilized IP networking infrastructure to provide localized processing, speedy information 

access, and remote data replication. 

9 

SYMMETRIX SYMMETRIX 

SRDF/FC 

CONNECTRIX 

SRDF/FC


SRDF and EMC TimeFinder SRDF functionality can be combined with that of EMC TimeFinder to create expanded 

capabilities. EMC TimeFinder is used to create locally resident, point-in-time, mirrored copies of 

active volumes called “Business Continuance Volumes” or BCVs. While production applications 

continue to perform at full capability and capacity, BCVs can be used for other business purposes. 

For example: application testing with real data, on-demand data warehouse loads and refreshes, or 

running batch processes, such as backups. 

With SRDF installed, the BCVs can be created at either local (source), remote (target), or both 

types of Symmetrix sites. SRDF maintains full disaster recovery/business continuity even as these 

other operations proceed, ensuring information availability and simultaneously working with 

TimeFinder to enhance enterprise productivity and business acceleration. 

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Symmetrix (A) Symmetrix (B) Symmetrix (C) 

FC/AL 

Point to Point ESCON 

SRDF and Symmetrix systems can support AS/400 systems with the full suite of Symmetrix features and 

AS/400 Environments benefits. EMC CopyPoint enabling software that runs on AS/400 systems and affords Information 

Protection to data on EMC-connected Symmetrix. 

When used with SRDF, CopyPoint reduces nonproductive AS/400 system time to a minimum 

by allowing a second AS/400 the ability to offload many operational requirements such as 

point-in-time backups, batch processing, report generation, application testing, and data 

warehouse loading. Contact your EMC representative for complete details on the use of SRDF in 

AS/400 environments. 

IP 

ESCON 


Chapter 2 

SRDF Uses and Applications 

Overview As businesses become more global, applications grow significantly larger. A superior information 

protection solution, one that provides not just data safekeeping and disaster recovery capabilities, 

but also business continuity and acceleration is a necessity. 

To address this need, companies and government agencies are increasingly implementing solutions 

based on remote mirroring technologies. Remote mirroring is capable of making data available in 

less than an hour in the case of a disaster (versus typical tape recoveries of 24 to 72 hours), and with 

data current as of the last completed transaction. 

Remote mirroring reduces the time, costs, and data recovery efforts associated with traditional 

disaster recovery methods. System restoration times are minimized and data loss prevented so that 

data is recovered at the exact point of failure and in an expedient manner. Users gain the ability to 

continue their business operations in the event of planned outages such as daily backups, scheduled 

maintenance, and data center migrations or consolidations. The financial impact of 

both unplanned and planned events and their severe business disruption can be minimized or 

negated altogether. 

EMC’s Symmetrix Remote Data Facility, SRDF, accomplishes remote mirroring by connecting 

intelligent storage systems that reside locally or thousands of miles apart, independently of host 

processors. Introduced in 1994, SRDF is the leader in its market with thousands of licenses 

installed worldwide. With the recent additions of Fibre Channel connectivity, Virtual Private 

Networks using the Internet Protocol (IP) to traditional SRDF, EMC also expands your 

opportunities for business acceleration. 

Disaster Recovery, When a disaster occurs and the decision is made to utilize a disaster recovery site, many activities 

The Old Way must take place. The recovery site must be accessed and networks and telephones must be switched 

to the new site. The most recent tape copies of the operating systems, libraries, databases, and 

catalogs from the off-site vault must be retrieved and transported to the recovery site. And finally, 

the tape copies must be restored to disk, which may take days. This is not the most expedient 

method, but is the most widely used practice in the world today. Any method that shortens this 

cycle is obviously of great interest to disaster recovery planners. 

Disaster Scenarios Disasters may occur for any number of natural or man-made causes. Protection is required to 

recover from earthquakes, floods, fires, hurricanes, protracted power outages, destruction of the 

primary processing facility by terrorist activity, or any of hundreds of other causes including 

database corruptions and programming failures. 

11


Disaster Recovery Sites The disaster recovery plan must ensure that an alternative site is identified which meets the 

planner’s requirements with respect to: 

• Distance from the primary site 

• Communications capability 

• Processing power 

• Storage capacity 

• Accessibility for the required personnel 

Depending on the nature of the expected events that would cause a disaster, the site may be within 

yards of the primary site or separated by hundreds of miles. In the case of a fire, a recovery 

environment behind a firewall in the same building may suffice. In the event of an earthquake, a 

whole region may be devastated. Defining and verifying the physical site is a relatively easy process. 

Investigation and negotiation ensure that the required infrastructure is in an appropriate place and 

sufficient for the task. 

Traditional Techniques Various techniques have evolved for protecting information from natural and unnatural disasters. 

for Data Recovery Several of the more prominent are listed here. 

Store the Tape Copies It is a normal part of day-to-day operations in most data processing facilities to take backup copies 

at a Secure Site of critical data, libraries, and databases to enable ‘rapid’ restoration in the event of a problem. 

Typically, two copies are made, one stored on-site and the second stored off-site in a secure facility. 

Copies of data, generally on tape reels or cartridges, are usually stored in a secure facility, offsite 

from the primary processing facility. The tape cartridges are produced, typically overnight, and 

transported to the storage facility. This process alone introduces significant time delays in the 

currency of any backup data. The tape copy may have gone through a cycle similar to that below: 

• Database quiesced at midnight 

• Copy taken (4 to 6 hours) 

• Tapes stacked for shipment to secure site 

• Transport calls at 10:00 a.m. 

• Tapes driven to secure site 

• Tapes are secured at noon 

Thus the tape copy that is stored at the secure site may be several hours old (12 in the above 

example), and represents the current best starting point for recovery in the event of a disaster. 

When required, the tapes must be retrieved and transported to the recovery site. This generally 

means delays of many hours for the following functions to occur: 

• Select the appropriate recovery tapes from the secure site (2 to 4 hours) 

• Transport to the disaster recovery site (2 to 4 hours) 

• Restore to disk (8 to 18 hours) 

• Roll forward databases to best recovery level (6 to 12 hours) 

• Resume application processing 

12 


In the above scenario, it will have taken at least 18 hours to get the environment prepared to where 

it was before the disaster. Missing information and data, with consequent business risk, is 

the potential result of this scenario. Outages of this duration will clearly be intolerable in the 

new E-economy. 

Create the Tape Copies The time taken for retrieval and transport can be eliminated by actually writing the tapes at the 

at the Recovery Site recovery site using channel extenders and tape silo facilities. This clearly delivers an advantage in 

that the retrieval and transport of the tapes at the time of disaster is eliminated. However, the tapes 

must still be restored to disk, which is the most time consuming activity in the recovery process. 

The latencies associated with tape-based recoveries are simply too long. 

Data Copies on Disk Advances in channel extender facilities ó whether SCSI, ESCON, IP, or Fibre Channel — and 

host/server communications have facilitated keeping two copies of data available on disk in 

real-time mode. 

Using the Host/Server One method involves using the host/server to write data to both local and remote disk. This raises 

to Create the Copies several issues of resource consumption, currency of data (Is the data real-time or copied to disk at 

specific moments in the daily cycle?) and performance impact on daily operations, as well as 

implications on application maintenance if the copy facility is embedded in user programs. 

Another technique involves the host/server transmission of transactions as they occur. This second 

capability gives the user the option of storing the transactions on remote disk for later, relatively 

rapid, application to a copy of the database environment, or of direct application. In either event, 

CPU resources are still utilized and performance impact and cost issues are significant. 

Disaster Recovery Testing Typical disaster recovery testing involves manually intensive recovery drills, complex procedures, 

and business interruptions. In contrast, with SRDF IS staff can simply switch to the remote site at 

any time. Testing can be performed during normal business operations, a significant time and 

cost-saving option. For businesses serving global markets that operate on a 24 x 7 x 365 schedule, 

ensuring the highest level of data availability with no downtime is especially critical. 

Business Continuity Major impediments to business continuity exist that are mundane in nature and considered normal 

business and operational practices. These involve outages from nightly backups, new application 

testing, database loads and refreshes, and hardware and software upgrades. However, in today’s 

highly competitive and often global environments, businesses can ill afford the loss of productivity 

that is associated with these outages. Fortunately, with SRDF, such outages are no longer necessary. 

Business continuity planning must deal with all the challenges to system availability. Plans and 

processes must be put in place to: 

• Backup data without shutting down enterprise systems 

• Nondisruptively make duplicate copies of databases as required 

• Nondisruptively load data warehouses as frequently as required 

• Accomplish application upgrades without shutting down those applications 

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Eliminating the Standard information management practice is to conduct regularly scheduled information 

“Race to Sunrise” backups. With today’s global enterprises, this practice has become anything but routine. 

Applications have grown larger, backup windows have grown smaller, and any downtime results 

in potential revenue loss. SRDF eliminates the race to sunrise while allowing business operations to 

run continuously. Scheduled backup operations or new application testing is performed from the 

target Symmetrix data while normal operations are continuously running on the source 

Symmetrix. All the while, information is safely protected, available, and expanding its earning 

power. For many businesses, the SRDF payback is measured in just days. 

Loading Data Warehouses All too often conventional data warehouse loads and refreshes occur infrequently, when no other 

business-critical functions are in process. SRDF rectifies this situation and gives analysts and 

management personnel access to the latest information from which to plan business strategies and 

take advantage of immediate opportunities. Using SRDF remote copy volumes, data warehouses 

can be loaded and refreshed at more frequent intervals while normal operations to support the 

enterprise proceed nondisruptively. 

Scheduled Maintenance SRDF enables business operations to continue during scheduled site maintenance, such as 

operating system upgrades, host/server upgrades, and environmental disruptions. After 

applications are switched to a remote site, normal operations continue using the remote copy of 

synchronized application data. 

Data Center Migrations Data center migrations occur for many reasons, including: 

• Moving to a new building 

• Company move to a new site 

• As a result of a corporate reorganization 

• As a result of a corporate merger or acquisition 

From a data point of view, the migration involves: 

• Identifying a specific time for the move, typically the least busy time on a low-activity weekend 

• Shutting down applications 

• Copying all data and libraries to tapes 

• Transporting either the disk or tape copies to the new location 

• Installing the disk or restoring the tapes 

• Executing appropriate data validation processes, if required or desired by the user 

• Resuming applications 

14 


Clearly, the implication is an extended application outage, often as much as 20 or 30 hours or 

more. As the cost of application downtime grows, the financial impact of such a move can be 

considerable. SRDF reduces the size of the outage taken for the switch to the new data center to less 

than an hour by: 

• Remotely mirroring the application data and libraries beginning days or weeks prior to the move 

and keeping the local and remote copies synchronized with minimal performance impact 

• Performing data validations at the new center prior to the cutover, while applications are still 

running at the original site 

• Running the applications until the moment of cutover 

• Shutting down the application in the old site 

• Restarting the applications at the new site 

Workload Migrations The fundamental consideration for workload migrations is minimizing the outage taken by an 

application as its data is moved to the host/server where processing is to occur. Reasons for moving 

workloads include: 

• A different host/server is better suited to running the application 

• Application competency is superior in a different location 

• Merger and acquisition activity at the corporate level calls for the least disruptive absorption of a 

workload by an existing facility 

SRDF provides the means to support these activities without disrupting normal operations 

AS/400 Applications As with any mission- or business-critical application, customers using AS/400s require higher levels 

of data protection than in less sensitive environments. SRDF can provide that extra level of 

protection with no additional operational management or host system overhead. These critical 

environments need to conserve all the precious production time they can. EMC CopyPoint 

provides AS/400 customers a way to protect vital resources and extend the production day 

while still completing necessary data backups, batch processing, etc., without consuming any 

system overhead. 

EMC’s CopyPoint software gives AS/400 enterprises the ability to significantly enhance their 

operational productivity while also achieving strengthened protection against outages. 

15 

Primary 

Source Symmetrix 

SRDF LINK 

Target Symmetrix 

Recovery


At the time of a backup, the production AS/400 (source) application is quiesced and the AS/400 

main storage is flushed to clear all active data from the AS/400 memory. SRDF remote mirroring at 

the destination (target) Symmetrix partition is suspended. The entire quiesce/flush/suspend process 

takes just a few minutes. Then the production AS/400 can continue its production applications. 

With the SRDF link suspended, the backup, using CopyPoint, can commence from the second 

AS/400. Because Symmetrix offers protection for the source data, full business continuity is 

maintained even while SRDF mirroring is suspended. 

Once the backup is completed, SRDF mirroring is restored, and the source and target data volumes 

are automatically resynchronized by the Symmetrix with no AS/400 system overhead. 

Growing Your SRDF over IP presents new opportunities for growth by capitalizing on e-focused business trends. 

Business with SRDF Take advantage of SRDF’s remote mirroring capabilities to replicate data such as mail system 

indexes and mail boxes, establish application test beds, deliver widespread management reports 

and distribute software. The lower telecommunications costs of IP-based SRDF can be reinvested 

to make wider or growing data more accessible, increasing the volume of data that is remotely 

protected, and optimizing localized applications or data. 

SRDF Over IP Optimizes Carried over IP, data is a replicated mirror, using delayed synchronization techniques. Applications 

Information Deployment for which this delayed synchronization are appropriate include data warehousing, development 

systems, mirrored web sites, multi-hop, bulk data movement, and data center consolidation. 

SRDF over IP lets you accelerate, simplify, and optimize your business-critical information 

processes and resources in innovative, cost-effective ways. For example, if you need to deploy 

mirrored Web sites, refresh data warehouses or migrate applications and databases, SRDF Over IP 

can create copies of the data and transmit them over IP-based Virtual Private Network to a remote 

Symmetrix system. 

Using an IP network for data replication can significantly lower operational costs, since an IP 

communications infrastructure likely exists. Other uses for SRDF’s mirroring capabilities using the 

IP network might include replicating mail system indexes and mail boxes to establish application 

test beds, deliver widespread management reports, and software distribution. 

SRDF Over Fibre Channel Applications that would particularly benefit from a SRDF FC topology are those that require 

Increases Throughput synchronous, realtime mirroring. Information for financial transactions, such as for brokerage 

accounts, banking, and mortgage servicing, and critical production data such as for 

telecommunications, databases, and manufacturing systems are obvious examples of applications 

that would benefit from SRDF over FC. High bandwidth, efficiency, low delays, and low overhead 

are familiar advantages of FC. In campus mode, within 10 kilometers, SRDF over FC will run 

synchronously, with significantly added throughput over traditional connection methods. 

16 


Chapter 3 

SRDF Detailed Description 

SRDF Principles At the simplest conceptual level, SRDF is mirroring (RAID level 1) of one disk device (source) to a 

of Operation second device (target) in a physically separate Symmetrix system over ESCON or other high-speed 

communication links. The distance separating the two Symmetrix systems can vary from within 

the same room to thousands of miles. 

As with RAID 1, if either disk in the mirrored pair fails, the requested data is instantly available 

from its mirror copy. No disruption to normal operations occurs. Once the disk again becomes 

available (through repair, replacement, or operational procedure), the newly available member of 

the pair can be resynchronized with its mate. 

Because the mirrored volumes reside on separate Symmetrix systems, unique capabilities result 

over and above the information protection features of a remotely mirrored RAID 1 system. The 

duplicate volumes can be temporarily disconnected from the mirroring scheme and used 

for nondisruptive: 

• Backup and restore operations 

• Development and testing of applications from third-party software providers 

• Timely loads and refreshes of data warehouses and data marts 

• Complex queries and report generation 

• Disaster recovery testing 

SRDF Hardware SRDF requires a minimum of two Symmetrix systems — one source system and one target system. 

Components Additionally, there may be one server system sending information to multiple target systems and/or 

multiple sources sending information to one target. SRDF requires a minimum of two Remote 

Link Directors (RLDs) or Remote Fibre Directors (RFDs) to be installed in the Symmetrix systems, 

both source and target. The Remote Link Director is a two-port channel adapter, microcodeconfigured 

as the link between the Symmetrix systems. Symmetrix supports up to eight RLDs 

depending on the Symmetrix model in use and the business continuity requirements. Remote Fiber 

Directors are two-port channel adapters, again installed in pairs for redundancy on both 

Symmetrix systems. The maximum number of RFDs varies by Symmetrix model. The following 

figures schematically illustrate typical Symmetrix SRDF connectivity. 

Hardware component usage between two Symmetrix units in a uni-directional configuration 

17 

SYMMETRIX A 

CACHE CD CD RLD 

DD DD RLD 

S1 S3 S5 S7 

S2 S4 S6 S8 

RA1 

RA1 

RA2 

RLD 

RLD 

RA2 

SYMMETRIX B 

CD CD CACHE 

DD DD 

T1 T3 T5 T7 

T2 T4 T6 T8


Multi-hop, an SRDF Extended Distance solution, involves three Symmetrix systems. For more 

information on this solution, please see page 23. 

18 

UNIX Server 

server 

264 

SYMMETRIX A 

MVS Host 

SCSI 

FC-AL 

ESCON 

Symmetrix 

CD CD 

RLD RLD DD DD 

RLD 

RA1 

RA2 

RLD 

RA1 

SYMMETRIX C 

RA2 

T1 T2 S1 S2 

RLD CD CD RLD RLD 

SRDF/ 

ESCON 

DD DD 

T1 T3 T4 S2 

T2 S1 T5 S3 

CNT 

USED 

RLD 

SYMMETRIX B 

IP-BASED 

Network 

Router Router 

Adding 

IP 

Suport 

to T3/E3 and 

ATM 

CNT 

USED 

SRDF/ 

ESCON 

Symmetrix 

SRDF can run over Virtual Private Networks with addition of partner-supplied hardware that 

encapsulates SRDF traffic and makes it ready for transmission via IP. 

RA1 

RA2 RA2 

RA1 

CD CD 

DD DD 

S3 T3 T4 T5 

CACHE 


Dramatic throughput increases are possible when SRDF runs across Fibre Channel networks. 

SRDF Implementation EMC Professional Services are available to help you receive optimum value from your 

implementation of SRDF. Specific planning and design services tailor your SRDF solution to your 

particular enterprise business continuity requirements. 

SRDF implementation and maintenance is both easy and cost-effective. No special application 

coding is required and no CPU overhead is incurred. SRDF functions completely independently 

from the host processor and operating system. As a result, all major mainframe and open systems 

hardware and software platforms are supported. 

SRDF setup and installation parameters are accomplished through the Symmetrix integrated 

service processor. Optional EMC ControlCenter software may be used to configure and manage 

SRDF implementations by means of an easy-to-use GUI or via a command line interface 

for automation. 

An SRDF implementation involves the following components: 

• A minimum of two Symmetrix enterprise storage systems. In the case of SRDF over IP or FC, must 

be specific models of Symmetrix 3000, 5000, or 8000 series. 

• Symmetrix Enterprise Storage Platform (ESP) software (required for installations with a mix of 

Symmetrix 3000 and 5000 systems). 

• Remote Link Adapters (RLAs) or Remote Fiber Directors (RFDs). 

• Microcode license for SRDF for each Symmetrix. 

• Communication links between Symmetrix systems. 

• For use with the IP protocol, a channel extender must be used on each end. 

19 

SYMMETRIX SYMMETRIX 

SRDF/FC


Installation and Planning Several configuration guidelines must be met in order to ensure SRDF properly executes in a 

specific environment. Successful implementation of SRDF involves choosing the appropriate 

features that meet the business continuity/disaster recovery and performance needs of 

the enterprise. 

The following aspects should be considered when choosing the types of data and volumes to be 

remotely mirrored: 

• Databases, logs, catalogs, system residence volumes, and program libraries are excellent candidates 

for SRDF mirroring. 

• Page, spool, and work datasets are poor SRDF candidates as they are easily recreated on the 

target location. 

Every SRDF installation is unique and therefore it is important to thoroughly discuss the business, 

configuration, and application performance requirements with an EMC representative. 

Supported Environments Since SRDF runs on Symmetrix, it is operating system independent. Thus, any host environment to 

which a Symmetrix system is attached is supported. The following chart lists the currently 

supported host hardware and operating system platforms. Consult EMC for updates to the list. 

20 

Multihost Support 


Vendor System Minimum 

21 

Operating System 

Bull ® Escala AIX 4.2.1, varies by model 

Compaq ® /DEC ® AlphaStation and AlphaServer Digital ® UNIX ® V3.2A, 

Series 3000 AXP, Models 300-900, OpenVMS ® 6.2 or higher, 

1000, 2000, 2100, 4100/4200, 

8200, and 8400 

Windows NT V3.5.1 

Data General ® Aviion ® 5500 (88K-based), DG/UX ® 4900/5000 (Intel-based) 

R4.11 MU03 

Data General ® AV4900, AV5900 (Pentium ® ) Windows NT ® V4.0 

HP ® 3000-900 Series MPE/ix 5.0 

HP 9000/700 Series: 725/100, 735/99, HP-UX ® 9.05, 

735/125, 755/99, 755/125, 

715/100XC, C-Series, J-200, J-210, 

210CX, 250 

HP-UX 10.20 

HP 9000/800 Series: E, F, G, H, I, 

T500, D, K 

HP-UX 9.04, 10.20 varies by model 

IBM AS/400 ® (all 9406 including RISC, OS/400 ® except Model B) 

V3R2 

IBM RS/6000 AIX ® 4.2.1 

IBM SP2 ® AIX 4.2.1 

IBM S/390 ® & S/370 Any 

IBM Symmetry ® 2000 & 5000 DYNIX/ptx ® 2.1.5 

IBM NUMA-Q DYNIX/ptx ® 4.3 

Intel ® -Based All Novell ® 3.12, 

Servers Windows NT 3.5, 

or OS/2 ® 2.1 

NCR ® 34xx, 35xx, 36xx, 41xx, 45xx, 

3600AP, 5100 (S, C, M) 

UNIX SVR4 2.03.01 

Siemens ® -Pyramid Nile ® Series Datacenter ® OSx 94D079.6 

RM 1000 Datacenter OSx 95M079 

Reliant UNIX V5.43C0053 

Silicon Graphics ® Challenge ® S, L, DM, & XL IRIX ® 5.3 

Silicon Graphics Origin 200 and 2000 IRIX 6.4.1 

Stratus Continuum 400 Series HP-UX B.10.20.1 

Sun ® SPARCserver and SPARCcenter 10, SunOs ® 20, 1000, 2000 

4.1.3, 

Solaris 2.3 

Sun UltraSPARC Workstations and 

UltraSPARC Servers 

Solaris 2.5.1 

Unisys ® Clearpath IX, NX OS/MCP, OS/2200 

Note: Contact your local EMC sales representative for specific hardware and software 

configurations. 

In addition to a wide range of platform support, SRDF is configurable into multiple Symmetrix 

environments such that one Symmetrix serving as an SRDF target system can support up to 16 

other Symmetrix systems serving as source systems. Generally the number is less than 16 as this 

would necessitate a physical disconnection of one Symmetrix from the remote link adapters in 

order to gain access to a server processor to resume business operations.


22 

SYMMETRIX 

SOURCE H 

SYMMETRIX 

SOURCE G 

SYMMETRIX 

SOURCE F 

SRDF Campus Solution In the Campus solution, the Symmetrix systems are connected with ESCON fiber from as little as 

3 meters to 66 kilometers. For distances between 0 and 3 kilometers, no converters or repeaters are 

needed with multimode fiber connected directly to the Remote Link Adapters (RLAs). If the sites 

are more than 3 kilometers apart, then standard ESCON channel directors, repeaters, and 

converters must be used in 20-kilometer segments. 

SRDF over Fibre Channel will run synchronously in campus mode up to 10 kilometers, from the 

host Symmetrix to the target Symmetrix or Connectrix switch if in the middle. 

An EMC 9191 device is used to: 

• Support multimode-to-singlemode conversion and singlemode-to-singlemode signal regeneration. 

• Support SRDF at full ESCON speed. 

SYMMETRIX 

SOURCE A 

SYMMETRIX 

TARGET 

SYMMETRIX 

SOURCE E 

SYMMETRIX 

SOURCE B 

SYMMETRIX 

SOURCE C 

SYMMETRIX 

SOURCE D 

• Support source and target Symmetrix systems located at distances between 3 and 26 kilometers. 

For customers who require greater distances, three EMC 9191 devices can be used to extend the 

path up to 66 kilometers. 

The Campus solution supports all SRDF modes of operation and bi-directional SRDF capability. 

Bi-directional SRDF capability means that both source and target Symmetrix systems can act as 

both source and target for each other. This is particularly useful when the sites are to be used for 

backup sites as well as for other applications. Dual mode, a variant on Bi-Directional mode, is 

also supported. 


SRDF Extended Extended Distance solutions are appropriate for wide area protection and for areas where fiber 

Distance Solutions cannot be installed; for example, where data centers are further than 66 kilometers apart or local 

restrictions will not allow the placement of fiber. Extended Distance solutions can also be used to 

link data centers to a centralized private recovery site or any of several commercial regional 

disaster recovery service providers. 

In Extended Distance solutions, the RLA’s output is still to ESCON fiber. This ESCON fiber is 

connected to a telecommunications protocol conversion unit, which is provided by any of several 

independent vendors. These network boxes convert the ESCON protocol to the appropriate 

telecommunications protocol, whether T3/T1, E3/E1, or ATM. Network boxes available from 

Computer Network Technology, InRange Technologyís GEN, StorageTek (formerly NSG), and 

Computerm Corporation are currently supported. Some feature data compression. For further 

information, contact the independent vendors directly. 

SRDF FarPoint SRDF FarPoint is a high performance feature that optimizes both the long distance (>15 km) 

Campus and Extended Distance solutions. SRDF FarPoint significantly increases performance by 

eliminating queuing and increasing communication line utilization. This results in a more costeffective 

solution and, in some instances, allows the same level of performance with fewer lines. For 

more detail on SRDF FarPoint, see “SRDF FarPoint Operations” later in this chapter. 

SRDF Multi-hop Capability Another time- and cost-saving Extended Distance offering is SRDF’s multi-hop capability. Multihop 

enables SRDF users to mirror only data that has changed since the last update to a Symmetrix 

system in a third location. Symmetrix to Symmetrix transmissions are made synchronously in the 

local or campus area, whereas delayed synchronization modes are used for long-distance segments. 

Utilizing EMC TimeFinder, this capability is ideal for cost-effectively mirroring data long-distance. 

By copying only the changed tracks, less bandwidth is consumed, performance is enhanced, and 

transmission times are shorter. Multi-hop mirroring to the third site can take place during off-peak 

times or over lower cost transmission lines or via IP-based Virtual Private Networks. Recurrent 

monthly line costs can be dramatically reduced, quickly recouping the investment in a third 

Symmetrix system. 

SRDF’s multi-hop capability decreases line transmission costs by mirroring only the tracks changed 

since the last update and taking advantage of lower cost transmission lines or IP-based VPNs. 

23 

Symmetrix Source 

Synchronous 

Mode 

Intermediate 

Symmetrix Target 

Adaptive 

Copy Mode 

Using FarPoint 

Final 

Symmetrix Target 

Los Angeles Phoenix New York


SRDF over IP for SRDF over IP takes advantage of two fundamental characteristics of IP-based VPN networks. 

Extended Distances VPNs are often underutilized and they do not require a dedicated circuit. This latter point means 

that operational telecommunications costs (usually priced on a per circuit mile basis) can be 

dramatically reduced. 

SRDF Modes of Operation SRDF offers flexibility in specifying how data transfer is performed between source and target 

volumes. The following modes of operation and configuration options can be intermixed and 

operate simultaneously in the appropriate manner in order to achieve a proper balance among 

performance, communication link cost-effectiveness, and timeliness of information 

synchronization required. 

Primary mode choices are: 

• Synchronous Mode 

• Semi-synchronous Mode 

A Secondary mode is: 

• Adaptive Copy Mode 

Each logical volume must be configured in one of the two primary modes. The decision on which 

primary mode to select is based upon such factors as performance and distance. 

In addition, there are several configuration options that can be specified for Symmetrix volumes. 

These are: 

• Consistency Group Utility for MVS 

• Consistency Group Feature for Open Systems 

• Domino Option 

• SRDF FarPoint 

• Invalid Tracks 

Synchronous Mode Synchronous Mode is most appropriate for data that must be written in two locations before the 

application is to continue. This ensures that a second copy of the data, accurate up to the last 

transaction, is immediately available for use. Synchronous Mode provides mirroring of data 

between the source Symmetrix and the target Symmetrix system. In this mode, data is first written 

to the source system and then to the target system. Next the application is notified that the I/O is 

complete. AS/400 systems are supported only in Synchronous Mode. 

When writing to a remotely mirrored volume, the following sequence of events takes place in Synchronous 

Mode: 

Step 1: Data is written to the cache of the local Symmetrix and an entry is placed in the 

SRDF FIFO (First In, First Out) queue for the updated data. 

Step 2: The first available RLA takes the first entry in the queue and moves it across the 

link to the remote Symmetrix cache. 

24 


Step 3: The remote Symmetrix acknowledges the receipt of the data. 

Step 4: The I/O complete signal is presented back to the host/server, which initiated the I/O 

request. 

In Synchronous Mode, SRDF writes data simultaneously to the cache of both source and target 

volumes, in real time, before the I/O is complete. SRDF over Fibre Channel is used in local and 

campus configurations and may optionally connect through the Connectrix family switches in 

pass-through mode. 

Semi-Synchronous Mode Semi-synchronous operation is used to mask any performance impact that could result from I/O 

propagation delays. Semi-synchronous Mode writes data to the source system, completes the I/O, 

and then synchronizes the data with the target system. Since the I/O is completed prior to 

synchronizing data with the target system, this mode provides an added performance advantage. A 

second write will not be accepted on a volume until the target has been synchronized (hence, 

not asynchronous). 

By presenting an earlier I/O complete signal to the host/server, the host/server can continue 

processing reads to the logical volume. Most applications do a read before they do a write. This 

implementation successfully masks the I/O elongation that is created by the propagation delay to 

the target system in a pure synchronous mode. 

When writing to a remotely mirrored volume, the following sequence of events takes place in 

Semi-synchronous Mode: 

Step 1: Data is written to the cache of the local Symmetrix and an entry is placed in the 

SRDF FIFO queue for the updated data. 

Step 2: An I/O complete signal is presented back to the host that initiated the request. 

Step 3: The first available RLA takes the first entry in the queue and moves it across the 

link to the remote Symmetrix cache. 

Step 4: The remote Symmetrix acknowledges the receipt of the data. 

25 

CPU A 

1 4 

CD CD 

CACHE 

SYMMETRIX CONTAINING 

SOURCE (R1) VOLUME 

RLD 

RLD 

3 

2 

RLD 

RLD 

CACHE 

CPU B 

CD CD 


TARGET (R2) VOLUME


In Semi-synchronous Mode, SRDF writes data to the source system, completes the I/O, and then 

resynchronizes with the target system. 

Adaptive Copy Mode The Adaptive Copy Mode of operation is useful for data center migrations or for migrating large 

blocks of data from one place to another or when using SRDF over IP. When choosing this mode of 

synchronization, the user should be aware that data is not transferred in a serialized manner. 

Therefore, Adaptive Copy Mode is not a prime choice for real-time recovery. 

In Adaptive Copy Mode, the user specifies that a source volume’s primary mode of operation be 

suspended. Data is transferred from the source volumes to the remote volumes without waiting for 

an acknowledgment and allows a lag between source and target volume of a specified number of 

I/Os. This allows SRDF to manage the Adaptive Copy volumes at a lower priority, thus enabling 

applications using that volume not to encounter propagation delays while data is transferred to the 

remote site. 

26 

CPU A 

1 2 

CD CD 

CACHE 


SOURCE (R1) VOLUME 

If the number of I/Os at which the threshold is set should exceed the specified number, SRDF 

suspends its asynchronous state and reverts back to its primary mode of operation until the 

number of unsynchronized I/Os are below the threshold. When the I/O threshold is re-established, 

SRDF reverts to Adaptive Copy Mode again for the pair. 

Consistency Groups In MVS and open systems environments, SRDF users also have the option of using the Consistency 

Groups to provide database coherency protection for volumes spread across multiple Symmetrix 

systems. The Consistency Group capability, available with latest microcode versions, maintains 

database coherency across an SRDF configuration by monitoring data propagation from the 

source devices (R1) in a defined consistency group to their corresponding target (R2) devices. 

RLD 

RLD 

4 

If data from one or more source devices in a Consistency Group cannot reach their corresponding 

target devices, it suspends all data flow to the consistency group’s target. This ensures that a 

consistent database — up to the point in time of data propagation failure — exists on the remote 

side of the configuration for use by applications. 

I/O to the local Consistency Group devices can still occur while data flow to the targets is halted. 

Although these updates are not immediately sent to the remote site, they are propagated through 

usual SRDF operation once the affected CG links are again operational. 

3 

RLD 

RLD 

CACHE 

CPU B 

CD CD 


TARGET (R2) VOLUME 


Domino Option By specifying the Domino option for the mirrored pair, any failure to complete write operations to 

both volumes in the relationship will cause the source volume to present an ‘intervention required’ 

status to the operating system. This in turn makes its way back to the driving application and alerts 

the user to the fact that the mirrored write did not complete and gives the user the option of 

preventing further activity. 

SRDF FarPoint Option SRDF FarPoint significantly enhances Synchronous Mode performance for SRDF Extended 

Distance solutions. SRDF FarPoint allows I/O from multiple logical volumes to be serially 

transmitted on the SRDF link by a single Remote Link Director (RLD), up to one outstanding I/O 

per logical volume. This enables the SRDF communication link to be more fully utilized depending 

on the distribution of application I/O write activity across multiple logical volumes. If an 

acknowledgement is not received from the distant end, SRDF FarPoint will resend data for that 

element and all that follow in the pipeline. 

The major advantages of using SRDF FarPoint for Extended Distance solutions are twofold: 

• Bandwidth utilization is improved at long distances because there can be multiple I/Os serially 

transmitted by an additional RLD at any time. Thus, as line distance increases, this results in better 

utilization of line bandwidth. 

• The SRDF I/O write operation will spend less time waiting in the queue to be serviced, resulting in 

higher I/O performance and lower average response times. 

SRDF FarPoint is available for Extended Distance implementations and Campus implementations 

greater than 15 km. 

Invalid Tracks Attribute The Invalid Tracks attribute is implemented at the logical volume level. This prevents a target 

volume from becoming ready when it is not fully synchronized with its source. 

SRDF Management SRDF can be managed: 

• Through the Symmetrix service processor (EMC service personnel only). 

• Through EMC ControlCenter, SRDF/TimeFinder Manager option. 

EMC ControlCenter is an optional software product that offers unparalleled ease-of-use in 

implementing, reconfiguring, monitoring, and terminating SRDF configurations. With EMC 

ControlCenter SRDF users can perform such functions as: 

• Query the status of the SRDF relationships (drives, links) 

• Modify the options for each logical drive pair (Synchronous, Semi-synchronous, Adaptive Copy, 

Invalid Tracks) 

• Issue SUSPEND or RESUME commands for mirroring activity for individual drive pairs or entire 

SRDF subsystems. 

A comprehensive list of the SRDF commands and their functions may be found in the appropriate 

technical documentation. 

27


Chapter 4 

SRDF Usability Considerations 

SRDF Features SRDF features provide users with unsurpassed information protection capabilities — capabilities 

and Capabilities that not only protect vital information assets, but also enable users to put those assets to 

competitive advantage. This chapter describes many of these features and capabilities as well as 

how SRDF employs them in typical scenarios. 

Sequential Data Updates When using Synchronous or Semi-synchronous mode, updates occur sequentially across the SRDF 

Across the Link communication links. When a WRITE to an SRDF-participant volume takes place from a host, the 

data is moved into the cache of the local controller. SRDF maintains a queue, called the SRDF 

queue. This queue contains pointers to data which has been written to the local cache and that must 

be moved to the remote Symmetrix. Entries are made to this queue as the data arrives from the host. 

The data is moved from the queue in FIFO fashion, ensuring that data sequencing is preserved as 

data is moved between the SRDF participants. 

Local and Remote Mirrors With SRDF the user may have two, three, or four copies of the same volume in combinations of 

of the Same Volume mirroring or BCV volumes. This high availability capability enables flexible solutions such as 

point-in-time backup of data. 

SRDF and RAID-S SRDF fully supports the RAID-S capability of EMC Symmetrix systems. RAID-S is EMC’s 

Compatibility exclusive high performance parity-based RAID protection scheme. RAID-S protection can be 

intermixed with EMC Mirroring (RAID 1) or non-RAID-protected volumes in an SRDF 

environment, both locally and remotely. 

Dynamic Sparing Symmetrix Dynamic Sparing capability can be used to provide protection for SRDF mirrored 

drives. Dynamic Sparing can be used: 

• To augment the protection provided by local and remote mirrors by providing yet another level of 

safety in the event of a volume failure. In this combination, the already impressive availability 

profile afforded by optional full local and remote mirrors (four addressable copies of data!) is even 

more so. 

• As a less costly manner of providing protection, but with the realization that dynamic sparing alone 

may not provide full protection in all circumstances. 

Source/Target Switching This capability enables reconfiguration of synchronized SRDF volumes causing R1s (the source) to 

become R2s (the target) and R2s to become R1s. It results in a reversal of the data flow 

and facilitates continual disaster recovery readiness during workload migrations. Specific 

benefits include: 

• Swapping of specific host/server applications may be remotely mirrored, providing continued 

disaster recovery readiness in the event of either site going offline after an R1/R2 swap. 

• Allows host/server hardware and/or operating system upgrades without compromising disaster 

recovery readiness by continuing to make the data available with R1/R2 swapping. 

• Eliminates the need to perform SRDF source site resynchronization because remote mirroring will 

continue between the swapped SRDF sites (assuming the SRDF source site is online). 

Note: Contact your EMC representative for a list of platforms supported for Source/Target 

Switching. 

28 


Example of source/target switching 

Source Control of Target SRDF commands can be performed at target locations without a host being present. Point-in-time 

backups and disaster recovery testing at the target site can be remotely managed from the source or 

production site. The primary source site can also create the Business Continuance Volume (BCV) 

that serves as the source for mirroring to a third location in a multi-hop solution. In addition, 

TimeFinder commands can be executed over SRDF links. 

HP MetroCluster Hewlett-Packard’s MC/ServiceGuard with MetroCluster software and EMC SRDF is an 

integrated, open systems disaster-tolerant solution enabling geographically dispersed HP-UX 

clusters to be combined into a single, manageable system with automatic failover of applications. 

When a site becomes inoperable due to a system failure or a disaster event, application package 

switching occurs. This action automatically transfers control of the affected application to another 

HP 9000 system located in a secondary site, while also automatically read/write-enabling remotely 

mirrored EMC disk devices associated with the transferred application. 

HP MetroCluster for EMC SRDF allows cluster support between sites up to 40 kilometers with an 

intersite link, which is used to provide heartbeat communication between cluster nodes. HP 

Continental Clusters extend the distance limits while operating in a similar manner. 

29 

Without R1/R2 Swapping 

SRDF Source SRDF Target 

R1 R1 R2 R2 

With R1/R2 Swapping 

SRDF Source SRDF Target 

R1 R2 R1 R2


Potential Events The balance of the chapter discusses typical “what if” scenarios and how SRDF manages them. 

Local or Remote Volumes If the user has implemented local as well as remote mirrors for the volume, then most types of 

“Out of Service” events are quite transparent to the user. 

If the drive that failed is not locally protected, the application will continue, utilizing the RAID-1 

capability of SRDF. Applications continue by reading data from and writing to the survivor in 

the pair. When repair is effected nondisruptively, automatic resynchronization of the drives 

takes place. 

Link Breaks When one or more SRDF links break, applications continue running, but performance will likely 

be impacted because all I/O activity is then routed across the remaining links. 

If all links break, the Domino option may be invoked, which will prevent applications from 

running against the local Symmetrix. If this loss of availability is not desirable, Consistency 

Groups for MVS or open systems can be utilized to ensure integrity on the remote side while 

maintaining application availability at the local site. Upon link resumption, the changes that 

occurred on source volumes can be copied automatically to the target volumes, while normal 

application I/O activity continues. 

Return to Source Site If after processing at the recovery site, as a result of a disaster or a test, you wish to return to the 

primary site, you can do so regardless of whether the original or new equipment is in place. Restart 

processing begins almost immediately. 

The following steps are required: 

• Link the Symmetrix devices together in the originally defined configuration 

• Restore target volumes to the source volumes 

• Restart applications on the source side 

It is not necessary to have full resynchronization before starting applications. This is because 

SRDF knows where valid data resides. As the application processes data, it will be pre-emptively 

moved from the target to the source if it is requested prior to having been moved. While processing 

is in progress, SRDF can resynchronize all the data from the target volumes to the source devices. 

Returning to “normal” operations is accomplished with almost as little pain as recovering from 

the disaster using SRDF flexibility. 

Or, you can switch the roles of source and target, as described on page [layout assigns page] of this 

chapter, to accommodate extended unavailability of the primary site. 

30 


Given that SRDF allows read-only access to the remote copy of data, that copy may be used for 

backup. The challenge is to establish a point-in-time that gives the backup consistency. This is 

accomplished as follows: 

• When the time to perform backups arrives, quiesce the application for a short time and ‘flush the 

buffers’ so that a consistent set of data, indexes, pointers, etc. exists on disk (both local 

and remote). 

• Issue a SUSPEND command to SRDF for the volumes that are to be backed up. This command will 

allow the applications to continue accessing the local (source) copy of data, but not transmit the 

changes to the second (target) copy. However, the changes will be tracked for later transmission. 

• Resume the application processing at the local site. 

• Take a copy of the selected volumes, using a second processor or a second LPAR accessing the 

target volumes. 

• When the copy is complete, issue a RESUME command for the volumes. This will allow SRDF to 

examine the internal entries for the volumes, and resynchronize the two sets of data by copying 

only the changed data across the links. 

This technique has the potential to deliver hours of effective, profitable application time to the 

installation. The gains in application availability may justify the cost of SRDF in their own right 

and disaster recovery capability may be an added bonus. Of course, for this application, the second 

copy may be on the same computer room floor as the primary copies or at a remote site. 

Synchronization and There are several ways in which the source and target sites may be out of synchronization with 

Resynchronization each other. These are: 

• At the inception of the SRDF relationship, when initial synchronization is being established. 

• In the event that a source or target volume fails and application activity continues using the 

surviving volume. (After repair of the failed volume, resynchronization is required.) 

• In the event that all physical links are inoperative between the sites. (This may be deliberate 

or accidental. In this case, the applications may continue running against the source volumes with 

resynchronization taking place after the links are restored.) 

• In the event that the user issues a SUSPEND command against specified or all volumes. (In this case 

the applications continue running against the source volumes, with resynchronization taking place 

after the RESUME command is issued for the SUSPENDed volumes.) 

Use of Track Tables SRDF does not keep a copy of every change to a given track. As data is written to a track, only the 

latest copy is stored. Within the Symmetrix, a track table exists. This table contains an entry for 

every track in the defined environment, describing: 

• The location of the track on disk. 

• Whether the track image is currently in cache and if so, where. 

• Demographic data (dates, etc.) about the track. 

• Whether the track image is synchronized with its internal (mirror) or external (target) pair. 

31


As a track changes and synchronization does not take place (failed volume, absence of links, 

SUSPENDed operations), the changed track indicator is maintained. Consequently, a track may 

change once or a thousand times in an interval, and only one copy will be stored. The cache is not 

filled with historical aged tracks awaiting application to the mirror. Once the track table entry for 

a track is marked, the track itself may be destaged to disk by the normal cache management 

routines. When it is necessary to perform the resynchronization of a changed track, that track is 

copied from cache or retrieved from disk to the local cache if it had been destaged. 

In addition to resynchronization, use of track tables also enables mirroring of only those tracks 

that have changed since the last update in a multi-hop mirroring solution. 

Performance The capability of placing data in two locations does have a performance impact, particularly for 

write operations. The performance impact may be lessened or even eliminated based on the mode 

of synchronization. The size of this impact is primarily a function of: 

• Write activity rate to mirrored volumes 

• Average data block size being updated 

• Distance between sites 

• Type of link (telephone line, ESCON, Fibre Channel, or IP) 

• Number of links 

• Mirroring mode (Synchronous/Semi-synchronous or Adaptive Copy) 

It is possible to model your data and its characteristics to determine the optimal SRDF 

performance for your site. 

Data Recovery Recovering from a disaster has several components. The target volumes must first be attached to 

the recovery host/server. Secondly, they must become read/write-capable. To accomplish this, a 

single Symmetrix command must be issued. This can be done: 

• By host-based SRDF management software 

• At the Symmetrix service processor by a local EMC field engineer 

• Remotely by the EMC support center, using a dial-in capability 

At this stage, the data can be accessed and complete data center operations can be restarted. 

Databases There are no special considerations for database environments apart from ensuring that all the 

data necessary for a consistent database is remotely mirrored. Restarting from the remote (target) 

copy of data (assuming all the appropriate data is remotely mirrored) is no different from restarting 

locally after a power failure. 

32 


Backup Using Remote Data Given that SRDF allows read-only access to the remote copy of data, that copy may be used for 

backup. The challenge is to establish a point-in-time that gives the backup consistency. This is 

accomplished as follows: 

• When the time to perform backups arrives, quiesce the application for a short while, and ‘flush 

the buffers’ so that a consistent set of data, indexes, pointers, etc. exists on disk (both source 

and target). 

• Issue a SUSPEND command to SRDF for the volumes that are to be backed up. 

• Resume the application processing at the local site. 

• Take a copy of the selected volumes using a second processor or a second LPAR accessing the target 

volumes. 

• When the copy is complete, issue a RESUME command for the volumes. This causes SRDF to 

examine the internal entries for the volumes and resynchronize the two sets of data by copying only 

the changed data tracks across the links. 

This technique can deliver hours of effective, profitable application time to the installation. The 

gains in application availability can justify the cost of SRDF in their own right, and disaster 

recovery capability may be an added bonus. 

This technique involves logical suspension of the remote mirroring function. Accordingly it is very 

strongly recommended that the remotely mirrored drives also be locally protected, exploiting 

the Symmetrix capability of having a drive both be remotely mirrored and locally mirrored via 

mirroring, RAID-S, or dynamic sparing. 

Read-Only Access As a general rule, the target volumes should be accessed after SUSPENDing mirroring. This has 

to Target Volumes obvious benefits with regard to data consistency. Using the second copy for point-in-time backup is 

a clear use for this facility. 

Read-only access to the target copy of data is available. Making a volume read-only is an attribute 

of Symmetrix. If an update I/O operation is attempted to a read-only drive, the operating system 

will encounter an error. Handling errors of this nature must be planned for by the user with regard 

to each operating system’s behavior. This facility must be used carefully and in no way represents 

generalized, full-function access to this data. 

SRDF Testing Validating the SRDF configuration can be extremely useful to customers in determining if they are 

mirroring all the necessary data elements. This test can be performed with minimal disruption to 

production and without staff travel. 

By suspending the SRDF link(s), a simulated disaster can be created. It is suggested that either a 

point-in-time backup be taken at this point from the target data volumes, or the TimeFinder 

product be used to create a separately addressable copy of data to be used for the disaster recovery 

test. It is then a relatively simple matter to run a test of the mission-critical applications at the target 

site. In so doing it is easy to identify if everything required is in fact being remotely mirrored and to 

verify that the database and application environment can be made ready in a simple, complete, and 

timely fashion. Users might also utilize SRDF’s Consistency Group feature for this purpose. 

This testing provides reassurance that SRDF delivers the best business continuity and recovery 

solution available, and renews confidence in the recovery plan itself. 

33


Chapter 5 

Symmetrix Software Solutions and Service 

Software Solutions Information Protection — EMC provides software solutions that maintain continuous data 

availability. The standard features of Symmetrix software solutions facilitate continuous data 

availability in the event of any major system component failure or power outage, and provide the 

ability to repair or replace the failed component without any interruption in operation. Symmetrix 

software solutions continually perform self-diagnosis to identify and correct potential problems 

prior to any disruption of data availability. Software products include: 

• Symmetrix Remote Data Facility (SRDF) 

• EMC TimeFinder 

• Symmetrix Data Migration Services (SDMS) 

• EMC Foundation Suite by Veritas and EMC Database Edition for Oracle by Veritas 

• EMC CopyPoint 

• EMC CopyCross 

Information Sharing — Symmetrix offers centralized, sharable information storage for supporting 

changing environments and mission-critical applications. This leading-edge technology begins 

with physical devices shared between heterogeneous operating environments and extends to 

specialized software that enhances sharing information between disparate platforms. These 

software solutions include: 

• Symmetrix Enterprise Storage Platform (ESP) 

• EMC Celerra 

• EMC InfoMover 

• Application Programming Interfaces 

Information Management — Symmetrix consolidates storage capacity for multiple hosts and 

servers and improves information management. The EMC ControlCenter family of products 

further enhances this efficient, consolidated storage approach. These optional software solutions 

include powerful GUI-based tools that simplify Symmetrix configuration, performance, and status 

information gathering and management. These products include: 

• EMC ControlCenter 

• EMC PowerPath 

• EMC Data Manager (EDM) 

The true power of EMC’s Enterprise Storage architecture comes with the synergy unleashed when 

customers utilize multiple EMC products together ñ allowing them to fully harness the power of 

their information for the first time and realize The EMC Effect. 

For more information about EMC Enterprise Storage solutions, contact your EMC sales 

representative. 

34 


Professional Services EMC Professional Services consultants provide a full range of services to enable you to extract 

maximum value from your information and achieve The EMC Effect. These services assist you in 

applying EMC Enterprise Storage concepts and capabilities to your business issues. The EMC 

approach enables you to put information at the center of your IT infrastructure so you can take 

control of your information and utilize it to your full advantage. 

Professional Services help you leverage EMC Enterprise Storage solutions, expertise, and resources 

to achieve success faster, more cost effectively, and with less risk. They enable you to: 

• Understand your current IT environment and take charge of it. 

• Create a more responsive, efficient, and flexible IT infrastructure with information at its center. 

• Share, protect, and manage critical information across the enterprise. 

• Deploy robust new enterprise solutions faster. 

EMC Professional Services personnel utilize EMC Storage Logic , a framework of EMC-specific 

and storage industry best practices that addresses all phases of an enterprise solution. Use of this 

framework ensures consistency and quality of deliverables and facilitates effective management of 

project budgets, schedules, and specifications. 

To help you build an IT infrastructure that takes full advantage of all your critical information, EMC 

Professional Services provides both strategic enterprise consulting services and practical enterprise 

software implementation services. Consulting services help you assess your current 

infrastructure in light of your requirements and sort through various options. Implementation 

services help you integrate a specific hardware and software solution into your unique environment. 

Enterprise Business Enterprise Business Continuity services protect and enhance your ability to generate revenue. They 

Continuity help you build an enterprise business continuity infrastructure that not only eliminates 

unacceptable downtime (planned and unplanned) but also creates new ways to capitalize on 

business opportunities to generate increased revenue and customer services. In short, Enterprise 

Business Continuity enables businesses to accelerate their entire operation. 

Enterprise Business Continuity services help you map and build your infrastructure to satisfy a 

range of business continuity requirements from high availability to mission-critical availability to 

continuous availability to disaster recovery. Assessment, planning and design, and software 

implementation assistance is available. 

Use of EMC Professional Services personnel for implementation enables you to quickly realize the 

advanced functionality of EMC software, while your in-house IT staff continues with other 

revenue-generating activities. A range of SRDF software implementation services are available, 

from basic software installation to complex integration projects that encompass the complete 

project lifecycle. Regardless of the level of complexity, EMC Professional Services personnel can 

address your unique technical, staffing, or timing requirements. 

In addition to software implementation services for such key business continuity products as 

SRDF, TimeFinder, and EDM, implementation services are also available to help you expand your 

information sharing, management, and protection capabilities by adding other EMC software 

products to your infrastructure. 

35


Enterprise Storage Enterprise Storage Architecture and Design is the most consultative practice. Its services give you a 

Architecture and Design broad-based overview of your IT environment and indicate where and how enterprise storage can 

— Building an enhance it. Assessments recommend specific storage-related initiatives that can help you compete 

E-Infostructure in your marketplace or otherwise increase the value and effectiveness of your infrastructure. An 

E-Infostructure employs EMC products so that customers are prepared to address the realities of 

the new E-based economy. 

Enterprise Storage Network Enterprise Storage Network services help you break out of current network limitations. They help 

you cost-effectively consolidate information from heterogeneous sources to offload data 

movement from your general-purpose network and improve information protection, sharing, and 

management. EMC experts in this new field of storage networking help you assess, plan, design, 

and implement an Enterprise Storage Network infrastructure that addresses today’s requirements 

and can grow with you in the 21st century. 

Support and Service The EMC Customer Support Center, headquartered in the United States, directly supports EMC 

software products. The following telephone numbers offer technical support: 

U.S. (800) 782-4362 (SVC-4EMC) 

Canada: (800) 543-4782 (543-4SVC) 

Worldwide: (508) 497-7901 (or contact the nearest EMC office) 

36

EMC SRDF 

where information lives 

EMC Corporation 

Hopkinton 

Massachusetts 

01748-9103 

1-508-435-1000 

In North America 

1-800-424-3622, ext. 362 

EMC2 , EMC, and Symmetrix are registered 

trademarks and TimeFinder, ControlCenter, 

E-Infostructure, SRDF, FarPoint, Enterprise 

Storage Network, Connectrix, and where 

information lives are trademarks of EMC 

Corporation. Other trademarks are the 

property of their respective owners. 

© 2000 EMC Corporation. All rights reserved. 

Printed in the USA. 6/00. 

Produced by EMC Global Communications. 

L759.2 

Product Description Guide 

www.EMC.com

Symmetrix Remote Data Facility (SRDF) Product Description ... - EMC

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