Hyper-V SnapShot Files – AVHD and VHD? What The ?
A couple of days ago I wrote about some issues I was having with one of my Hyper-V Virtual Machines and the snapshots that were associated with it causing my System Drive (C Drive) to run out of disk space. From what I was reading if you turn off the Virtual Machine in question a merging process will be conducted and the AVHD Files that are associated with the VHD File will merge together and form one file, a VHD one. This is what I was after.
I was reading and article by “The Virtual PC Guy’s” on Snapshotting under Hyper-V, and I determined that if I deleted the snapshots then the AVHD Files should be merged? But for some reason they did not merge?. Anyway the way to get these files merged to their parent VHD file (for me anyway) was to turn the VM off and just let the merge take place. Now I thought this process would take some time so I scheduled it for Friday night, my VM was a Microsoft Exchange Server, sureley no one would be checking their emails on a Friday Night !
I had 3 AVHD files that I wanted to get rid of, so I turned the VM Off and the “Merge in Progress” appeared in the Hyper-V Manager so I let it run it’s course. About 50 mins later the merge process was complete and 2 of the AVHD Files just VANISHED, great! but there was still one left? So I decided to turn the VM off again and what do you know another Merger was taking place, so again I left this happen and after it had completed the final AVHD File dissappeared and I was left with one VHD File, FANTASTIC!
One thing I learnt from this experience was that the VM writes to the AVHD Files and doesn’t appear to touch the VHD File (Parent File). I think I got myself into this situation because the Snap Shots were not deleted corectly. So now I am going to do some more testing on Hyper-V Snap Shotting and get a better understanding on how this works.
Keep Updated with this and more by SUBSCRIBING to My RSS Feed (The Big Orange Icon on the right), or via email by typing in your email address in the box and I will automatically send you my Blog Posts.
I had exactly the same issue, some missunderstanding and lack of documentation from MS let me think that the snapshot took a copy of the .VHD, but it simply doesn’t. Check my article out on :
http://www.gary-martin.co.uk
Gary Martin
2 Jan 09 at 5:12 am
[...] in a week or so, so I will be stepping up my migration of Physical Servers to Virtual ones using Hyper-V. I will be letting you know how that goes and how I think the best way of going about this is. I [...]
The Year to use Hyper-V and get Virtual - Windows 2008 Network Administrator | Windows Server Administration
27 Jan 09 at 12:01 pm
Hyper-v snapshots are nothing like the VMware snapshots; and unlike VMware MS does not recommend running productions server with snapshots. Only use snapshots prior to making major changes to the VM, incase something breaks. Also DC’s, Exchange, and SQL servers should never be running with snapshots on a regular basis. I have heard of server crashes that cause a VM to revert back to it’s orginal state with all changes since snapshots lost forever, Yikes.
Albecool
17 Apr 10 at 5:13 am