Thursday, July 17, 2008

RAID Alignment and VMware ESX 3i 3.5

Make sure to create your datastores from within the Virtual Infrastructure Client GUI, don't take what the ESX install CD creates (this means deleting any data stores created by the install CD).

It's because the Install CD creates the partitions on the standard Sector 63 starting position (31.5k into the drive. This isn't a proper multiple of any common RAID stripe size (2k, 4k, 8k, 16k, 32k, 64k, etc) so the partition ends up being out of alignment with the RAID stripe elements, and READ/WRITE performance will suffer.

This is all documented in a number of VMware documents.

Creating the partitions in VCI makes them start on sector 128 (64k into the drive), which lines up properly.

Questions on what RAID stripe size and what Windows Allocation Unit size to use will be in another post.

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