Specifications

© IBM Copyright, 2012 Version: January 26, 2012
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Summary of Best Practices for Storage Area Networks
a WWPN for a device, switches interpret the WWNN to designate all associated ports
for the device. Using the WWNN in a zone can cause multipathing issues where there
are too number of paths between a server and storage.
A possible refinement is to keep destinations isolated from each other in “single-initiator,
single-target” zoning. This is sometimes used in environments where it is common for a
single host to access multiple destination devices. While this provides some additional
measure of preventive isolation, it must be balanced with the additional administrative
overhead involved with the increased number of zones.
No matter which of the above zoning implementation methods is utilized in a SAN
environment, there can be exceptions to the rule. One such example involves clustered
servers which handle some portion of intra-node handshaking across the SAN fabric.
The IBM Subsystem Device Driver (SDD) can support up to 16 paths per virtual disk
with DS8000 devices. With SAN Volume Controller (SVC) disks, SDD supports up to
eight paths per virtual disk. However, optimal SDD performance is obtained with just
four paths per virtual disk. Similarly, other third party and native operating system
multipathing utilities can support various numbers of paths per volume, but most of
these utilities also recommend only four paths per volume.
Aliases can greatly ease routine zone management tasks. Aliases associate a human-
readable name with the long hexadecimal world-wide port name (WWPN) and are most
useful for sets of ports which are used in more than one zone definition. Aliases are
typically most used with storage system ports utilized as target(s). For servers, the
name of the zone itself is usually sufficient, so server aliases do not provide similar
benefits as do storage system aliases for an equal amount of effort.
Aliases will allow the incorporation of path sets, or a limited number of paths being
assigned to a single alias. For example, multiple paths to a given SVC IOGroup and/or
DS8000 storage system can be readily defined with a single alias in a zone definition.
With the creation of just a few such path set aliases, it will be easier to manually rotate
host connections between the different ports on a storage system and thus achieve
good workload balance among the storage resources while minimizing the work effort
by the SAN and storage administrators.
The key point is that zoning is an important method to balance the workload across
multiple ports for a given edge device, whether it is a disk storage system with dozens
of ports or a server with four ports. Balancing the workload across a storage system