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

► Consolidation
Another benefit is replacement of multiple independent storage devices by fewer devices
that support capacity sharing; this is also called disk and tape pooling. SANs provide the
ultimate in scalability because software can allow multiple SAN devices to appear as a
single pool of storage accessible to all processors on the SAN. Storage on a SAN can be
managed from a single point of control. Controls over which hosts can see which storage
(called zoning and LUN masking) can be implemented.
► Protection
LAN-free backups occur over the SAN rather than the (slower) LAN, and server-free
backups can let disk storage “write itself” directly to tape without processor overhead.
There are various AN topologies on the base of Fibre Channel networks:
► Point-to-Point
With a SAN, a simple link is used to provide high-speed interconnection between two
nodes.
► Arbitrated loop
The Fibre Channel arbitrated loop offers relatively high bandwidth and connectivity at a
low cost. For a node to transfer data, it must first arbitrate to win control of the loop. Once
the node has control, it is free to establish a virtual point-to-point connection with another
node on the loop. After this point-to-point (virtual) connection is established, the two nodes
consume all of the loop’s bandwidth until the data transfer operation is complete. Once the
transfer is complete, any node on the loop can then arbitrate to win control of the loop.
► Switched
Fibre channel switches function in a manner similar to traditional network switches to
provide increased bandwidth, scalable performance, an increased number of devices,
and, in certain cases, increased redundancy.
Multiple switches can be connected to form a switch fabric capable of supporting a large
number of host servers and storage subsystems. When switches are connected, each
switch’s configuration information has to be copied into all the other participating switches.
This is called cascading.
FICON and SAN
From a zSeries perspective, FICON is the protocol that is used in a SAN environment. A
FICON infrastructure may be point-to-point or switched, using ESCON directors with FICON
bridge cards or FICON directors to provide connections between channels and control units.
FICON uses Fibre Channel transport protocols, and so uses the same physical fiber.
Today zSeries has 2 Gbps link data rate support. The 2 Gbps links are for native FICON,
FICON CTC, cascaded directors and fibre channels (FCP channels) on the FICON Express
cards on z800, z900, and z990 only.
502 ABCs of z/OS System Programming Volume 3