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I have server 2008 that runs several virtual machines. Due to an error each machine was allocated with a lot of disk space.

I want to change the maximum size limit of the virtual machines but I couldn't find how using VMM or Hyper-V manager.

I've tried deleting all of the machine's snapshots but it still doesn't allow me to change the allocated disk space.

Is there a tool or option I'm missing?

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up vote 5 down vote accepted

Hyper-V manager does not do what you want to do, but you can resize disk images in System Center Virtual Machine Manager.

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Does SCVMM allow you to change the maximum size of a dynamic disk? If so, how? Or are you just talking about compacting a dynamic disk to reduce the current allocation? – Robin M Oct 26 '11 at 11:12

Assming you don't have access to System Center Virtual Machine Manager (in Moo's post above) the only way I know of to do this is the same way as you would a physical server. Try for a boot CD to resize the partition, then use Drive Snapshot or similar to backup the C: partition. Create a new vhd of the correct size, boot off a WinPE CD or similar and restore C: to the new vhd.

It's a lot less scary than a real server because you can just copy the vhds somewhere safe before you start tinkering with them. Also because the controller will just look like an IDE controller to the boot CD you don't have to worry about disk drivers.


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Were your VHDs created as dynamic or fixed size? If they are fixed, you should be able to convert them to dynamic, then run a compact on them to get down the actual physical disk space they are using.

If you want to reduce the amount of space the host operating system is allowed, you could reduce the size of the partition on the disk either within the guest OS or using a utility such as gparted. Then, when you run a compact in Hyper-V on the disk, it'll reduce the physical size used and shouldn't grow beyond the partition size since the guest won't be using the space you removed from the partition.

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