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We have determined that dynamic (expandable) VHDs in our Hyper-V environment are causing performance slowdowns and would like to start converting the vhds attached to about 600 VMs (about 150 win2k3, 450 win2k8) from dynamic to fixed.

The native utilities (GUI or PowerShell) require the VM to be shutdown and then it writes the configured size (not used capacity) of the dynamic VHD to the new fixed VHD.

We are dreading the downtime required for the long copies, and we will have to let the NetApp SAN array deduplicate the zero's (freespace) after each VM moves.

Ideally we'd like to use vhdtool (or NetApp's PowerShell cmdlet New-NaVirtualDisk) to create new 'empty' (non-zero'd) fixed VHDs, and then with the source VM online copy all allocated blocks from the old dynamic VHD to the new fixed VHD, followed by a final sync with the VM offline.

Ideas? Can ghost or some other software meet our needs?

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VM's OS and HyperVisor? (VHDs are used by Hyper-V and Xen, very different hypervisors) – Chris S Mar 2 '12 at 14:40
new-navirtualdisk means more then likely hyper-v and for new disks that will be the way to go. Also 600 vms whats the typical guest os version? What we found is that we had a bunch of w2k3 vms's that had poor disk alignment and that along with dynamic disks really screwed things up. – tony roth Mar 2 '12 at 16:32
wonder what would happen if you shutdown the guest mounted the vhd then created a new vm and selecting the mounted vhd as the source for you new disk. the destination would be fixed. Not sure if this would work or not. And I'm not sure what would be faster the normal conversion or this. – tony roth Mar 2 '12 at 16:46
or of if you'd run disk2vhd within the guest os and have it output to a share located on the host. this would leave the guest running and do the majority of the work but I'm not sure what format the vhd file is that disk2vhd creates. – tony roth Mar 2 '12 at 16:56
also hope it wasn't your idea to use dynamic disks, or is that why you are not responding cuz you already been shown the door! – tony roth Mar 2 '12 at 18:32

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