Disk alignment with ESX and Windows 2003 guest

I don't see contraddiction between what Powerlink is telling and what VmWare is telling... EMC is talking from its very special point of view (the storage point of view) and is asking you to align IOs (from storage point of view). If you are using RAW volumes, IO's will come from the virtual host (thus I ask you to align the virtual host). If you are using VMFS ios will come from ESX server (thus I ask you to align VMFS).
VmWare is talking from a higher pint of view. And from VmWare's point of view I ask you to align both VMDK itself (the virtual disk, inside the virtual host) and the whole VMFS (as EMC suggests).

My words exactly, in other words.

If it's needed it should have been added to the EMC doc as well.

Thanks for the answers.

Ulli can you please write me an email ?? delcorno_stefano at emc.com

Thank you...

I believe the command for Symmetrix volume devices allocated to a W2K3 SP1 host is

diskpart(5.2.3790)
create partition primary align=128

diskpar for W2K

This is because a Symm, cache slot boundary, which is one track covers 64 Blocks ¿32Kb¿

A RAID5 set Meta boundary, which is 4 tracks covers 256 Blocks ¿128Kb¿

For CLARiiON LUN¿s presented to a Window OS host the same command is

create partition primary align=64

When we discuss Storage on EMC array we view things from a Block perspective as opposed to Windows which always assumes disk sectors this reports a max of 255 heads, which counts from 0, = 254 as the last head.

And if the application that you are going to host on that volume is MS-SQL, then you have to format the drive with a 64k allocation unit size.

I understand all this stuff might became null and void with the introduction of Windows 7

ESX will align the partition of a datastore automatically when a LUN is formatted in VMFS from within the ESX Vi Client. You can confirm this by logging onto the console and issuing a fdisk -lu at the command prompt. Look at the starting value.

Also Microsoft has changed their recommendations for Disk Alignment. Their recommendation is now to create the alignment at 2048 since this will cover most array stripe sizes. See http://support.microsoft.com/kb/929491 for more details. You do not need to align the partition in Windows 2008 and later as the partition will automatically be aligned at 2048.

Now if the array manufacturer has a specific recommendation for an alignment offset to use in place of the Microsoft general recommendation that would probably be the best one to use as it will be array specific, but most likely the Microsoft general recommendation will be sufficient.

In ESX disks are automatically aligned when you add a new LUN to this host and you format it as VMFS. Within that VMFS you create VMDKs in which the MBR is created which is misaligned, so yes, you'd have to align that one ni the virtual machine.
So you align twice, although the ESX part isn't needed, since it's automatically aligned.

are you sure about that? I've read somewhere that all vmdk that are created using Virtual Center are automatically aligned, no need to manually align them unless you are presenting RDM.

....told you.....

I only did it for the free stuff

LOL

Well I just tested this by creating a VMDK on one of our ESX 3.5 clusters, and assigning it to one of my Windows VMs. The VMDK appears as just a raw unitiniliazed disk and if you create the partition through Disk Management the partition will be misaligned. So, as Rob said you have to use Diskpart.exe for VMDKs.

Thanks Aran, i just found that paper. We don't have to align VMFS datastores if they are created using VC, but we do have to align VMs. Thank you for correcting me.

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