ABCs of z/OS System Programming Volume 3 - IBM Redbooks

NVS cache
NVS is used to store a second copy of write data to ensure data integrity if there is a power
failure or a cluster failure and the cache copy is lost. The NVS of cluster 1 is located in cluster
2 and the NVS of cluster 2 is located in cluster 1. In this way, in the event of a cluster failure,
the write data for the failed cluster will be in the NVS of the surviving cluster. This write data is
then de-staged at high priority to the disk arrays. At the same time, the surviving cluster will
start to use its own NVS for write data, ensuring that two copies of write data are still
maintained. This ensures that no data is lost even in the event of a component failure.
ESS Model 800
The ESS Model 800 has a 2 GB NVS. Each cluster has 1 GB of NVS, made up of four cards.
Each pair of NVS cards has its own battery-powered charger system that protects data even
if power is lost on the entire ESS for up to 72 hours. This model has the following
enhancements:
► Model 800 allows 4.8 GBps of aggregate bandwidth.
► In the disk interface the ESS has eight Serial Storage Architecture (SSA) loops, each one
with a rate of 160 MBps for accessing the disks. See “SSA loops” on page 464 for more
information about this topic.
► ESS implements RAID-5 or RAID-10 for availability and has eight disks in the majority of
the arrays. See “RAID-10” on page 466 for more information about this topic.
► Four disks sizes of 18.2, 36.4, 72.8, and 145.6 GB, which can be intermixed. The ESS
maximum capacity is over 55.9 TB with a second frame attached.
ESS Model 750
The ESS 750 is intended for smaller enterprises that need the enterprise-level advanced
functions, reliability, and availability offered by the Model 800, but at a lower entry cost and
size. It is specifically designed to meet the high demands of medium-sized mainframe
environments, and for this reason it is closely tied in with the IBM z890 offering.
The ESS 750 has capabilities similar to the ESS 800. The ESS Model 750 consists of two
clusters, each with a two-way processor and 4 or 8 GB cache. It can have two to six Fibre
Channel/FICON or ESCON host adapters. The storage capacity ranges from a minimum of
1.1 TB up to a maximum of 4 TB. A key feature is that the ESS 750 is upgradeable,
non-disruptively, to the ESS Model 800, which can grow to more than 55 TB of physical
capacity.
Note: Effective April 28, 2006, IBM withdrew from marketing the following products:
► IBM TotalStorage Enterprise Storage Server (ESS) Models 750 and 800
► IBM Standby Capacity on Demand for ESS offering
For information about replacement products, see 8.16, “IBM TotalStorage DS6000” on
page 474 and 8.17, “IBM TotalStorage DS8000” on page 477.
SCSI protocol
Although we do not cover other platforms in this publication, we provide here a brief overview
of the SCSI protocol. The SCSI adapter is a card on the host. It connects to a SCSI bus
through a SCSI port. There are two types of SCSI supported by ESS:
► SCSI Fast Wide with 20 MBps
► Ultra SCSI Wide with 40 MBps
454 ABCs of z/OS System Programming Volume 3