Partition Alignment on Virtual Disks

RobertKaucher

Does it make any sense to align partitions on virtual disks? I am setting up a SQL Server test system that will very likely be moved into production. It is a VM and has 3 disks.

Disk 0 for the OS
Disk 1 for the SQL MDFs
Disk 2 for the LDFs.

Each disk is stored on a different data store. I am attaching Disk 2 to the iSCSI SAN as it has good sequential write performance.

I ask because I want to ensure this system is as performant as possible, but I will not have a lot of time to test my theory that I should perform standard partition alignment for SQL server on these two disks (1and 2).

tiersten

No idea if its worthwhile but I align partitions either way. Doesn't waste much space and its easier to do it at the start than later.

RobertKaucher

Jimmy May's PASS session on partition alignment | Brent Ozar - Too Much Information

Looks like we are right...

Claymoore

There is no need to manually align the disks. Both VSphere 4 and Server 2008 automatically align the disk partition with the underlying physical disk.

�� The alignment of your file system partitions can impact performance. VMware makes the following recommendations for VMFS partitions:

�� Like other disk-based file systems, VMFS suffers a penalty when the partition is unaligned. Using the vSphere Client to create VMFS partitions avoids this problem since it automatically aligns the partitions along the 64KB boundary.

http://www.vmware.com/pdf/Perf_Best_Practices_vSphere4.0.pdf

Partition Alignment
Most partitions are misaligned when they are created by using the Disk Management tool. Therefore, we recommend that you create partitions by using the Diskpart.exe tool instead. Aligning sectors to track boundaries can have performance benefits, depending on the storage. Always use the storage vendor's recommended setting, but if your storage vendor does not have a recommended setting, use 64 kilobytes (KB). When running Exchange 2007 on Windows Server 2003, we recommend that you use Diskpart to align the storage track boundaries on all Mailbox servers (including clustered mailbox servers), Edge Transport servers, and Hub Transport servers, regardless of the partition type you are using. For detailed steps about how to use Diskpart to align input/output (I/O) with storage track boundaries, see How to Align Exchange I/O with Storage Track Boundaries. You do not need to use Diskpart when running Exchange 2007 Service Pack 1 (SP1) on Windows Server 2008.

Partition Design: Exchange 2007 Help



There's a definite performance penalty if you don't do this, which is why both OSes now do it automatically.

RobertKaucher

Claymoore wrote: »

There's a definite performance penalty if you don't do this, which is why both OSes now do it automatically.

Thanks, Claymoore. I was aware of this, but when I create a new partition a still do it by hand with diskpart. I suppose I'm a little old school that way. I imagine I can stop doing that now...