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I am creating a VM using Hyper-V on Windows Server 2008.

I am creating a new VHD on which to install the guest OS. Can that VHD be a dynamic disk, or does it have to be a fixed disk with pre-configured a size (e.g. 40Gb) before attempting install of the guest OS?

The guest OS will also be Windows Server 2008.

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3 Answers

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Yes, it is possible to install an OS to a dynamic VHD. We do it all the time (with Windows Server 2008).

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Thanks Adam.... – jmsmcfrlnd Jul 21 '09 at 22:00
Please be aware that for mission critical servers if you have intensive disk IO you are best to use a fixed sized VHD or use a Pass Thru Disk. Search for HyperV Pass Thru Disk for more information – Wayne Jul 22 '09 at 0:37
Thanks Wayne. This is all currently for development purposes. – jmsmcfrlnd Jul 22 '09 at 14:10
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I'm not aware of anything that would prevent you from installing the OS on a dynamic VHD.

Having said that I'm more familiar with ESX than Hyper-V :-)

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Have you successfully installed a guest OS on a dynamic VHD under Hyper-V? – jmsmcfrlnd Jul 21 '09 at 21:03
Yes, but this was over a year ago when Hyper-V was still in beta. – Richard West Jul 21 '09 at 21:05
Are you having a problem doing this? Or are you just asking if this is possible before trying it? – Richard West Jul 21 '09 at 21:07
Just wanted to ask before I waste time doing it. But no answer arrived fast enough...so I just did it and it works fine. – jmsmcfrlnd Jul 21 '09 at 21:56
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Yes, Hyper-V supports installing a guest OS on a dynamic VHD.

I just did it.

During the install process, I also had to setup a partition and format that partition. I chose the maximum size of the disk as my partition size, and I formatted the disk before selecting that partition as the target for the Windows Server 2008 installation.

I checked the available disk space on the physical drive during install, and it appears that the full size is not allocated immediately, but the expanding works as expected.

For example, my maximum size if 40Gb, and the size during install was down around 10Gb, and increasing as the install copied more files.

My goal is to have the smallest possible system drive for my VM, and yet, always have it expand as necessary if I have to install some programs there.'

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