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I have a Windows 2008 Datacenter server where I plan on creating dozens of VMs all using the same base Windows 2003 OS with some preinstall components and updates.

I was wondering,

1) What are the pros and cons to creating a parent VHD and using Hyper-V differencing disks to create multiple VMs that all share the same parent VHD. I anticipate that this would make creating new VMs based on that image incredibly easy.

2) If differencing disks are created, can the parent VHD be modified and have all the children continue to operate properly including the new changes. For example, could I install a Windows update on the parent VHD and all of the child VMs would automatically have that update applied as well (since the parent disk has changed)?

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up vote 1 down vote accepted

1) The differencing disk can be used to create a base image for multiple images from the same base operating system. Another usage would be similar to the snapshot feature to leave the base image and constantly recreate a child from the base image state. Also new VMs can be created much quicker by skipping the os installation part.

2) No. You cannot modify the parent partition and expect the children to be changed too. You can use SysPreped base images for such scenarios and update them instead. You have to deploy the OS with the SysPrep image afterwards but it would also be much quicker then a "normal" setup.

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