Specifications

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Summary of Best Practices for Storage Area Networks

For systems in high availability SAN environments, individual hosts will have multiple

paths to their respective storage volumes. Without multipathing utilities, many operating

systems would treat each path as a completely separate and unique resource even

though the end storage resource was the same in all cases. Multi-pathing

utilities/functionality are typically inserted into the IO path between the physical HBA’s

device driver and the operating system’s kernel, or logical volume manager, to “hide”

the details of multiple paths and only present one logical instance of each storage

volume. Another purpose of these utility applications is to silently handle a path failure

while normal IO operations continue.

However, multi-pathing can also experience the situation of “too much of a good thing”

by having too many paths between a host and a storage resource. As the number of

paths increases, the load on the CPU by the multi-pathing application can increase

significantly. One misunderstood fact is that doubling the number of paths between a

host and a given storage volume does not mean the total usable bandwidth has also

doubled. This observation is due to the computing needs of multipathing algorithm as it

makes use of the additional paths.

One condition which has been observed too many times within the SAN Central team is

a lack of coordination between server and SAN/storage administrators concerning HBA

maintenance. The historical experience has been a matter where the server

administrator considers HBA firmware updates as a function of the SAN/storage

administrator since the HBA is part of the SAN. Conversely, the SAN/storage

administrator considers HBA maintenance activities to be in the purview of the server

administrator since the HBA is located within the server. The key point and best

practice guideline is that the administrators need to arrive at a mutually agreeable

means where one, or both, are responsible for routine HBA maintenance actions.

8 Change Management

“Change Control” is one of the most discussed concepts in the management of

Information Technology. There are entire international standards dedicated to defining

it, and very expensive and complicated software created to implement it. However, in

practice, change control often ends up being implemented in ways that do little to

actually make the environment operate better.