WS2012 Hyper-V – Virtual Hard Disk (VHD) Block Fragmentation

The Performance Tuning Guidelines for Windows Server 2012 document is available and I’m reviewing and commenting on notable text in it.

This is a small but important note in the document:

Just as the allocations on a physical disk can be fragmented, the allocation of the blocks on a virtual disk can be fragmented when two virtually adjacent blocks are not allocated together on a virtual disk file.

The fragmentation percentage is reported for disks. If a performance issue noticed on a virtual disk, you should check the fragmentation percentage. When applicable, defragment the virtual disk by creating a new virtual disk with the data from the fragmented disk by using the Create from Source option.

Hmm, I’ve MSFT for more information on this one; I would have thought that we could defrag the LUN that the fragmented VHD was on, rather than create a whole new VHD.  I’ll update this if I get an answer.

One thought on “WS2012 Hyper-V – Virtual Hard Disk (VHD) Block Fragmentation”

  1. Hello…

    Well thx for sharing this important info.. should be more visible.. may be lots of people is looking for the wrong bottleneck.. lol
    till now i have been supposing the same as you.. but now i guess.. what to do.. lol
    whenever a vhd needs frag. create a new one from source??!!?? LOOL days are made of 24 hours not 48..

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