Hyper V Tutorials - 7 - How to Compact or Reduce size of Virtual Hard Disk (vhd ) in Hyper V
Compacting a virtual hard disk can use a large percentage of processor resources. We recommend that you do not perform this operation on a production computer. Compacting a virtual hard disk requires enough space to temporarily store the compacted file and the uncompacted file. This is because Virtual Server compacts a virtual hard disk by creating a new, compacted virtual hard disk and then deleting the original, uncompacted disk. If there is not enough space to complete the process, the problem is recorded in the Virtual Server event log.
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