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Hyper-V VM running off avhd and not vhd

Posted on 2014-02-07
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Last Modified: 2014-11-12
I virtualized a physical box some time ago and it has been running fine on Hyper-V 2012. I could create, delete and merge snapshots and the avhd files would disappear. Now I notice that I have no snapshot listed in settings for this server but there is one on the Hyper-V host and according to settings for this guest, it is now attached to the avhd as the data drive and the regular vhd is not listed in settings, tho it is still on the host where it belongs.

The avhd has the GUID name appended to what the vhd was named and is only one-third the size of the vhd. The server is running fine and there are no issues for the users.

How do I get rid of the avhd file and get the vhd back as the primary, and only, drive?
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Question by:LarryDAH
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Mahesh earned 2000 total points
ID: 39842985
Have you checked that you don't have even single snapshot left for the server ?
If you do not have any snap shot of server, it should show you empty
Can you please post VM settings snap here with respect to snapshot please.

if this is not the case and If you power off the server, during start it will give you error that HDD not found most probably and in that case you need to attach original VHD again as per my guessing

Mahesh
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Expert Comment

by:Cliff Galiher
ID: 39843234
.avhd files are any time of disk that is dependent on a parent vhd disk. While this most often means a snapshot, they can also be intentionally created separately through the disk creation wizard of Hyper-V, and is created when one chooses to create a "differencing disk."  It operates in very similar fashion as a snapshot. All changes are written to the differencing disk, but the base disk is still required for proper functionality.

You can use the disk convert option in Hyper-V to merge a differencing disk into its parent. It is a different wizard than merging a snapshot, obviously, since no shapshot exists. But what it does under the hood is essentially the same.

More info:

http://blogs.technet.com/b/yungchou/archive/2013/01/23/hyper-v-virtual-hard-disk-vhd-operations-explained.aspx
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Author Comment

by:LarryDAH
ID: 39843297
Well, we do not use differencing disks so I am not sure how it would have gotten created but I will try the merge feature in the link your sent in the off hours, thanks.
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LVL 59

Expert Comment

by:Cliff Galiher
ID: 39843304
As always, HAVE A BACKUP! If the circumstances that created your current state are unknown, there could be other surprises waiting for you. And a failed merge could be painful if you don't have a backup.
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Author Closing Comment

by:LarryDAH
ID: 39857118
Even tho the Hyper-V console did not show the the avhd file it was on the server. The problem turned out to be not enough disk space to finish the merge. It did not give an error that I could find, but when I created a new snapshot, then deleted while watching the server a message flashed about insufficient disk space then disappeared. Once I moved some stuff around it merged all the avhd files.
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