Auto shrink dynamic VHD while online in VMWare, HyperV, or Xenserver

Posted on 2011-03-15
Last Modified: 2012-05-11
Currenty I have been implementing HyperV on a small scale (1 or 2 servers max).  In this currenty senario I have two physical servers running Windows 2008 x64 both with the HyperV Role.  On one server I have a SBS 2008 VHD & a Windows 2003/SQL 2005 VHD.  On the other server I have a Windows 2003 x64 VHD for Terminal Services.

Disk speed is not a huge issue so all VHD are set up as dynamic expanding.  I have Backup Assist on each physical server that backs up to a rotation of USB drives that are plugged into each physical server.

So, here is my problem.  I have defrag set to run every Sunday on all VHD.  We have a daily backup that runs at night.

A)  These VHD keep growing in size even though the actual disk space usage in the VHD is just a fraction of the VHD size.  I understand how dynamic VHDs work, so I defrag, precompact, take offline, and then shrink.  A brutal all night process of downtime for each server.  The reason we don't use fixed VHD sizes is because I don't want to backup a 300GB VHD when only 150GB is being used.

Would migrating to a VMWare vSphere or Xenserver help fix this problem?  I dont mind scipting something that will auto shrink the VHD while the server is "online".

B) My Backups seem to take a long time using Backup Assist (6-7 hours for 500GB of information) on the server with SBS 2008 and SQL.  I have shadow copies enabled and setup for incremental windows imaging backups on the physical host.

Would migrating to a VMWare vSphere or Xenserver help fix this problem using deduplication or some other method?  

The budget is slim but I think I can squeeze some money for a migration if it resolves the issues above ($1000-2000) area.
Question by:tyty4u2
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LVL 17

Expert Comment

by:Sikhumbuzo Ntsada
ID: 35144581
Try the following with group policies:
LVL 17

Expert Comment

by:Sikhumbuzo Ntsada
ID: 35144594
Please ignore the previous post it was for another question!
LVL 17

Expert Comment

by:Sikhumbuzo Ntsada
ID: 35144622
Alright we use VMWare sphere 4.0, hosting 16 servers and growing, you have access to things like thin provisioning of vmdk / vhd in your case this allocates only the actual used space. Prety nice HA, DRS, vMotion and more.

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LVL 42

Accepted Solution

kevinhsieh earned 500 total points
ID: 35144723
You can try to stop defragmenting your VMs. My hyper-v VMs don't seem to grow the VHD like yours do.

You should load the Hyper-V hotfixes. There are lots, and several regarding shadow copy.

Performance with dynamic VHD under Hyper-V R2 is much better. You can move to Hyper-V Server 2008 R2 for free, But I don't know if it will work with your backup software.
LVL 42

Expert Comment

ID: 35144736
The hotfixes are not on Windows Update. You need to do a search for hyper-V hotfixes and you will find a technet page with all of them.

Author Comment

ID: 35144792
I have researched VMWare quite a bit lately and I am familiar with the technologies, but not so much as to how they function when implemented.  I am mostly concerned with VHD sizes and backup times.  I read some articles where VSphere suffered from the same issues with thin provisioning.  You have a 10GB VHD with only 10GB of data.  You add 10GB of data to the VHD and now the file size is 20GB.  You delete the 10GB of data and the VHD stays the same size.  Even though the files were deleted, the space they occupied isn't really empty.

I thought about throwing on SP1 now that it is out for Windows 2008.  Would the hotfixes be included in that release?  I have also thought about going to the free HyperV Server 2008 R2, but I must admit...I do like the GUI interface.  I have applied a hot fix or two about a year ago to fix some VSS issues.  It seems my VSS was timeing out after 10minutes.  I increased it to 20minutes and my backups are because successful more consitent, but I don't understand why the backups take so long.  Sure it is a lot of data, but not 7 hours worth if.  I am assuming it is backing up the full VHD everytime.
LVL 42

Assisted Solution

kevinhsieh earned 500 total points
ID: 35150259
My guess is that your backups are for the whole VM each and every time.

There is currently no technology to reclaim space from a thin provisioned volume. Microsoft is working with storage vendors on an API so that the filesystem can tell the underlying storage that specific blocks are no longer in use and can be reclaimed. This will probably take years to become widely available, and may require the next version of Windows.

If you are running Windows 2008 R2, then I believe that SP1 has all of the hotfixes. Otherwise, here is the list of all Hyper-V SP2 hotfixes. The page also has a link to the Hyper-V 2008 R2 hotfixes.

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