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Quelles sont les raisons possibles pour lesquelles Hyper-V ne peut pas compacter un VHD ?

ayi

I am hosting several virtual machines on a host running Hyper-V Server 2008 R2. The disks were originally provisioned on a different server (2008, not R2) about 16 months ago, and were migrated onto this server one year ago. Most guests are running Windows 7.
Recently I was comparing the VHD size to used space reported by the guest, and noticed that several machines had VHD files that were 50-100% larger than actually needed. So I decided to try compacting the VHD files to free up space on the host. I followed instructions I found on the internet, roughly as follows:
<ul>
<li>
Run CHKDSK in the guest machine
</li>
<li>
Run a defrag in the guest machine (Windows built-in defrag)
</li>
<li>
Shut down the guest
</li>
<li>
Open “Edit Disk…” tool in Hyper-V Manager
</li>
<li>
Select the VHD of interest and choose to compact it
</li>
</ul>
The first time I tried this, it worked flawlessly and reduced the size of my VHD by about 50%. But for the disks of every other guest, I get this error message:
<pre><code class="lang-auto">The server encountered an error trying to edit the virtual disk.

'The system failed to compact 'C:\example.vhd'. Error Code: The requested
operation could not be completed due to a file system limitation

</code></pre>
No guests have NTFS compression enabled. There are no snapshots of these disks. What else could be causing this error?
Edit: Bonus points for anybody who describes a solution to keep dynamic VHD sizes in check automatically.

ayi_2

Remove the shadow copies from the guest. That will do it!
<pre><code class="lang-auto">vssadmin delete shadows /all

</code></pre>