SQL Server with Mr. Denny

May 26 2011   2:00PM GMT

Running on EMC Clarion CX4 – Windows reports disks are not aligned, SAN admin says that because of caching, the partition alignment from windows does not matter (and SAN is setup per "best practices". Is this true?

Denny Cherry Denny Cherry Profile: Denny Cherry

Caching has nothing to do with disk alignment.  It sounds like your sysadmin should have gone to my SQL PASS pre-con.  All the caching does is accept the writes from the host into D-RAM instead of writing to the disk directly.

Now if the LUN is aligned on the array by setting the offset on the array side (which isn’t recommended as it makes LUN migrations within the array more difficult) then you want to leave them misaligned in Windows.  If however they are setup with a 0 offset within the array (which is the default) then they need to be aligned within Windows.

Denny

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