topic Disk Alignment in Microsoft Virtualization Discussions

Disk Alignment

andy_burge — Thu, 05 Jun 2025 07:29:17 GMT

Regarding disk alignment with NetApp Volumes and Hyper-V VM’s using VHD’s. If we select the LUN type as 'Windows server 2008', do we still need to adjust the offset when formatting the VHD’s virtual disk - before loading the OS for a Win2K3/2K8 VM? Also, do we need to adjust the offset when formatting the iSCSI logical drive on the Hyper-V host?

Our disk offset still looks incorrect once the VM is created (see screenshot - Disks info on a Win2K3 VM as VHD on iSCSI LUN), despite the LUN type being “Windows Server 2008” when created with ONTAP v.7.3.x…

Re: Disk Alignment

forgette — Thu, 16 Apr 2009 12:15:57 GMT

Hi Andrew,
Yes, the guest filesystem on the VHD file requires alignment. Also, the best practice is to used the 'fixed' type VHD format. The version of the OS dictates how much effort is required. For example Win2K, WinXP and Win2K3 use a starting offset which is misaligned by default. For these OS, you should follow the process outlined in TR-3747 (or any of the TRs below). Win2K8 and Vista use a properly aligned offset by default. The following technical reports have more information on this.

Best Practices for File System Alignment in Virtual Environments
NetApp and Microsoft Virtualization Storage Best Practices
Microsoft Hyper-V on NetApp Deployment Guide

Hope this helps,
-Eric

Re: Disk Alignment

andy_burge — Mon, 20 Apr 2009 17:15:23 GMT

Very clear...

Our environment - Server 2008 CORE Hyper-V host servers (without SnapDrive client installed), iSCSI connected to LUN's created with the "Windows Server 2008" LUN type using ONTAP 7.2.6.1 and utilizing the Fixed Disk VHD method for guest VM's. Our VM's are either Windows Server 2003 or Windows Server 2008.

Our disk alignment concerns - Our only guest VM's needing special attention in terms of making sure their boot disk is formatted with an offset divisible by 4,096 are the Server 2003 guest VM's. Whereas, all our additional virtual disks (VHD's) used as simple data disks and assigned to any guest VM's, need to be formatted so as to have the correct offset. Especially if these 'additional disks' are blank, pre-formatted Fixed Disk VHD's sitting in the VMM library, available for provisioning to new and existing VM's. Likewise for our blueprint guest VM's pre-loaded with Server 2003, sitting in the VMM library and available for provisioning as new VM's, especially need to have the correct offset as these VHD's will be replicated many times.

Thanks,

Andy