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

The ESS was the first of the Seascape architecture storage products to attach directly to IBM
System z and open system platforms. The Seascape architecture products come with
integrated storage controllers. These integrated storage controllers allow the attachment of
physical storage devices that emulate 3390 Models 2, 3, and 9, or provide 3380 track
compatibility mode.
Powerful storage server
The storage system is intelligent and independent, and it can be reached by channels or
through the network. It is powered by a set of fast RISC processors.
Snap-in building blocks
Each Seascape product is comprised of building blocks, such as:
► Scalable n-way RISC server, PCI-based. This provides the logic of the storage server.
► Memory cache from RISC processor memory.
► Channel attachments, such as FC-AL, SCSI, ESCON, FICON and SSA.
► Network attachments, such as Ethernet, FDDI, TR, and ATM.
► These attachments can also implement functions, that is, a mix of network interfaces (to
be used as a remote and independent storage server) and channel interfaces (to be used
as a storage controller interface).
► Software building blocks, such as an AIX subset, Java applications, and Tivoli® Storage
Manager. High level language (HLL) is more flexible than microcode, and is easier to write
and maintain.
► Storage adapters, for mixed storage devices technologies.
► Storage device building blocks, such as serial disk (7133), 3590 tape (Magstar), and
optical (3995).
► Silos and robots (3494).
Universal data access
Universal data access allows a wide array of connectivity, such as z/OS, UNIX, Linux, and
OS/400®, to common data. There are three types of universal access: storage sharing, data
copy sharing, and true data sharing, as explained here.
► Storage sharing
Physical storage (DASD or tape) is statically divided into fixed partitions available to a
given processor. It is not a software function. The subsystem controller knows which
processors own which storage partitions. In a sense, only capacity is shared, not data; one
server cannot access the data of the other server. It is required that the manual
reassignment of storage capacity between partitions be simple and nondisruptive.
The benefits are:
– Purchase higher quantities with greater discounts
– Only one type of storage to manage
– Static shifting of capacity as needed
The drawbacks are:
– Higher price for SCSI data
– Collocation at 20 meters of the SCSI servers
– No priority concept between z/OS and UNIX/NT I/O requests
Chapter 8. Storage management hardware 451