Specifications

www.ibm.com/support/techdocs 24

Summary of Best Practices for Storage Area Networks

unable to communicate to your disk arrays or mirror write cache because you have a

single congested link leading to an edge switch.

If at all possible, plan and design for the maximum size configuration the SVC

cluster could eventually reach. The design of the SAN can change radically for larger

numbers of hosts. Modifying the SAN later to accommodate a larger-than-expected

number of hosts will either produce a poorly-designed SAN or be very difficult,

expensive, and disruptive. This does not mean you need to purchase all of the SAN

hardware initially, just that you need to layout the SAN while keeping the maximum

size in mind. Always deploy at least one “extra” ISL per switch. Not doing so may

lead to consequences from complete path loss (this is bad), to fabric congestion (this

is even worse).

With the exception of a Stretched Cluster SVC solution, never split the two nodes in

an I/O group between different switches. However, in a dual-fabric configuration, half

the nodes ports must remain on the same switch with the other half of the ports on

another switch.

Unless two clusters participate in a mirroring relationship, all zoning should be

configured so that the two clusters do not share a zone. If a single host requires

access to two different clusters, create two zones, each to a separate cluster. The

storage zones should also be separate, even if the two clusters share a disk

controller.

If a FlashCopy mapping is created, where the source VDisk is a target VDisk of an

active Metro Mirror relationship, then this will add additional latency to that existing

Metro Mirror relationship (and possibly affect the hosts which are using the source

VDisk of that Metro Mirror relationship as a result). The reason for the additional

latency, is that the FlashCopy prepare disables the cache on the source VDisk

(which is the target VDisk of the Metro Mirror relationship), and thus all write I/Os

from the Metro Mirror relationship need to commit to the storage controller, before

the complete is returned to the host.

When connecting an SVC to a DS8000, there are several standard configurations

that should be used:

• 4-adapter/8-port configuration: 32 array max

• 4-adapter/16-port configuration: 48 array max (marginal configuration)

• 8-adapter/16-port configuration: >48 array max (or multiple SVC clusters)