Specifications

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Summary of Best Practices for Storage Area Networks

A SAN is a simple thing, a path from a server to a common storage resource. So,

where do the complexity and interoperability concerns originate? The first key point

to remember is that interoperability is based on the lowest common denominator for

features, functionality and available services.

Limited budgets and too few skilled people have pushed many organizations into

looking for short term solutions. When a new application or project appears, the

easy, inexpensive option is to simply introduce another server, whether it is a

physical or virtualized server is an implementation item. Now add storage to the

sprawl. Every server has two or four fiber Host Bus Adapters (HBAs) and a share of

the consolidated storage.

To make things more difficult, most SAN environments have servers from multiple

vendors, with decisions made on cost, suitability to a specific application, or merely

some administrator’s personal preference. Different vendor’s servers were tested on

very specific SAN configurations. Every server vendor has their own interoperability

matrix or list of SAN configurations that the vendor has tested, and as a little

understood fine point, the only configuration(s) which a particular vendor supports.

Further complicating matters, the configuration lists account for specifics such as:

• Operating system level

• Specific HBAs and the drivers for these HBAs

• Multipathing software

• Types and models of SAN switches

• Code level for these switches

• Storage subsystems and the microcode level that was tested

Because the SAN and storage are common to all servers, therefore, the

interoperability matrix for every server then has to be checked out and compared

before any change is made to the storage network, or even to individual servers.

A reasonably complex SAN could have servers from Sun™, IBM, HP, and Dell and

storage subsystems from the same or other vendors. There is no guarantee that

SUN, Dell, and IBM support the same level of SAN or disk microcode. Changes,

upgrades, or new implementations can be delayed for months, while waiting for the

different vendors to support a common code stream or driver. A best practices rule

for interoperability in SANs is that it is the manufacturer of the storage device that

defines interoperability. They do the testing that produces a matrix of supported

configurations, from the storage device to different types of server.