It seems like things aren't so clear when you are using a SAN and your storage administrator is simply carving LUNs out of a large disk group. Chances are high that the SAN disks on your server are operating across the same physical sets of spindles. I imagine this is even more the case when your SAN is using something like virtual disk/vRaid technology.

Michael Earl (11/21/2008)

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You are correct in that you lose the benefit if the SAN admin is carving three partitions out of a LUN that is using the same physical drive array.

Of course, your initial assumption "should" be wrong. Your admin should be carving these out of individual physical disk arrays. They often really need different RAID configurations. Log files have lots of sequential writes, data files have lots of reads and non-sequential writes, and backups - well it is often best to put those on cheaper, slower drives so you can afford to retain a few days or weeks of them without breaking the bank.

The best place for information on how the SAN should be configured is your SAN vendor. MSSQL configurations are extremely common these days. They should have done enough of these to know what configurations will suit your needs - assuming you give them enough information. Every SAN solution seems to be a bit different, so talk to your vendor.

Michael Earl (11/21/2008)

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Your admin should be carving these out of individual physical disk arrays. They often really need different RAID configurations.