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Merge .avhd to .vhd in Hyper-V

Posted on 2014-10-30
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Last Modified: 2014-11-23
Hi all, I am looking for some advice on the best way to manage a potential snapshot problem.

Last weekend I installed some MS updates onto a Windows 2008 R2 Hyper-V server VM, this server had a snapshot and once the updates installed the server booted. The snapshot merged, but the server would not boot again stating it could not find the .AVHD drive.  The drive it was looking for was the snapshot ID, this has totally been blown away following the potential merge.  Recovery steps are currently underway.

Checking my other installations I noticed the following, I have .AVHD files associated to a server running drives that actually has no snapshots listed.  This server has been rebooted to see if a merge happened but when it came up again (thankfully) the .AVHD files are still being used (see below).

Does anyone know the best (safe way) to merge these files?

Thanks in advance for any suggestions and advise :-)

Hyper-V-Server
Cluster-Storage-for-Server
Cluster-Storage
Cluster-Storage-data
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Question by:mercuriousu2
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5 Comments
 
LVL 78

Accepted Solution

by:
David Johnson, CD, MVP earned 250 total points
ID: 40414964
you are using a differencing disk which will always have a avhd.
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Author Comment

by:mercuriousu2
ID: 40415000
It does not on all of my other VM's running, not until such time as a snapshot is taken does the .AVHD appear.
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LVL 38

Assisted Solution

by:Philip Elder
Philip Elder earned 250 total points
ID: 40415012
How to merge is here: TechNet: Manually Merge VHDs.

Perhaps a PowerShell script was run to fire off a snapshot for each VM or they were set up with Differencing Disks to begin with using a base OS image?

Note that the method indicated requires VM downtime. Plus, you need enough storage for both source and destination files (depending on your CSV layout).

We usually pull the main file and one AVHD file at a time over to a standalone system with Hyper-V on it to run the merge process.
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Author Comment

by:mercuriousu2
ID: 40425710
Thanks for the comments, checking online I don't think this is a differencing disk though.

The VM has been in use for a few years and this has not been a problem before, I assume that the last snapshot taken at some point did not fully get shown on the interface?

This is what I see:
Hyper-V-Server-Snapshots.jpg

Although the snapshot is mentioned, the VM does not show it in the pane below the high-lighted running VM.

As this is a large production server, I think the test will be to not re-boot but to shut it down and then restart it.  I will do this at the weekend, this will allow time to first take a local backup and enable enough time to recover should anything actually go wrong.

Any suggestions to a good ADHOC local backup option on a Hyper-V, looking at Veeam?
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Author Closing Comment

by:mercuriousu2
ID: 40461543
Finally found time to shut down the server, I stand corrected as this was indeed a differencing disk.  It's the only one in our system that has been originally setup like this is appears.

At least I know there is not a bigger issue going on with this regarding missing snapshots not showing on the host!

Thanks for you time in looking as this.

Points shared :-)
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