DIsk Align - Need Some Help and Clarification

JAYJAYJAYUK — Thu, 05 Jun 2025 06:43:32 GMT

I have read various posts on the disk align issues and have 5 questions

First :

Are the following correct

- VMFS3 does NOT need to be aligned

- Windows 2008 VMs do NOT need to be realigned?

Second :

There are three levels of alignment -

1 - Guest OS

2 - VMFS

3 - Netapp

When you run the MBRAlighn tool - does the tool work at layers 2 and 3? I am assuming so ?

Three :

Would the following solution be valid to align disks

- Create a New VMFS using the VS Client

- VMotion off the VMs to the new datastore

Four :

There are many posts about the true benefit of aligning disks. It would appear that only high IO VMs would benefit from Disk Alignment? Is this true?

Five :

How can I confirm which of my VMs have alignment issue and how can I also validate that the Netapp [3270] does indeed have IOP overhead BECAUSE of disk alignment?

Many thanks!

Annabelle

DIsk Align - Need Some Help and Clarification

arash — Mon, 17 Oct 2011 18:00:22 GMT

Hello

Here are the answers to your questions :

First:

Q: VMFS3 does NOT need to be aligned :

A: The default offset of VMFS3, when created with the Virtual Infrastructure Client or VMware vSphere Client, is 128 blocks by default, which does not result in misaligned I/O. But keep in mind that here we are talking about the alignment of the VMFS file system on top of NetApp file system WAFL

Q:Windows 2008 VMs do NOT need to be realigned?

A: Windows 2008 VM's use GPT disks instead of MBR. So They do not need to be realigned after being created, but if you are moving a 2k8 VM from VMFS 2 or doing a P2V you probably need to realign your VMs

Second :

There are three levels of alignment -

1 - Guest OS

2 - VMFS

3 - Netapp

Q: When you run the MBRAlighn tool - does the tool work at layers 2 and 3?

A: Actualy it works on the -flat.vmdk file (Guest OS HDD) trying to fix the starting offset for your VM

Three :

Q:Would the following solution be valid to align disks

- Create a New VMFS using the VS Client

- VMotion off the VMs to the new datastore

A: No , thats not a resolution for realigning the disks . Alignment should occure on the starting offset of the guest OS (-flat.vmdk files)

Four :

Q: There are many posts about the true benefit of aligning disks. It would appear that only high IO VMs would benefit from Disk Alignment? Is this true?

A: No , Aligning misaligned VM's will increase the overall performance of the storage system not just the VM's with high I/O

Five :

Q: How can I confirm which of my VMs have alignment issue and how can I also validate that the Netapp [3270] does indeed have IOP overhead BECAUSE of disk alignment?

A: Using NetApp MBRAlign tools you can find out which VMs are misaligned ( MBR tools are no part of the VSC 2.1.1 which you can download from the NOW site for free)

Also here is a link to Best Practices for File System Alignment in Virtual Environments

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DIsk Align - Need Some Help and Clarification

DIsk Align - Need Some Help and Clarification