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Cold VHDs missing from Data Deduplicated storage volume

    Question

  • This has happened to us twice now. It seems as though whenever the deduplication garbage collection runs on our Server 2012 R2 Hyper-V host, the VHDs from all cold (Not turned on) VMs disappear.

    The VMs are still visible in Hyper-V Manager, but their disks are gone off the storage volume.

    Does anybody have any idea why this might be happening?

    Saturday, October 26, 2013 2:47 PM

Answers

  • Hi,

    Thank you for posting your question. This is indeed very interesting. There are no limitations for deduplicating volumes with turned off VM’s VHD/VHDX files. Live file support for dedup is only limited to VDI. Even if this would be somehow caused by dedup alone I would still understand any form of corruption, but files disappearing is very strange. One could turn on audit on the files; I would rather suspect an interfering driver able to interact on the IO stack. This could be anything installed from antivirus software to any backup solution, encryption software or basically any driver loaded.

    Thanks,
    Basar

    Monday, October 28, 2013 3:23 PM

All replies

  • It might not be related to garbage collection but all I have is this:

    Log at 3pm:

    Optimization job has completed.

    Volume: F: (\\?\Volume{46e4e2e1-3a97-11e3-80b7-b8ac6f7cc774}\)
    Error code: 0x0
    Error message: 
    Savings rate: 78
    Saved space: 619025970272
    Volume used space: 174212689920
    Volume free space: 825989345280
    Optimized file count: 19
    In-policy file count: 19

    Log at 4pm:

    Optimization job has completed.

    Volume: F: (\\?\Volume{46e4e2e1-3a97-11e3-80b7-b8ac6f7cc774}\)
    Error code: 0x0
    Error message: 
    Savings rate: 63
    Saved space: 300015559007
    Volume used space: 174164320256
    Volume free space: 826037714944
    Optimized file count: 11
    In-policy file count: 11


    Saturday, October 26, 2013 3:03 PM
  • Hi,

    There is no specific document state that we will have the issue that VHDs will be missing when running Deduplication. However from the article "Plan to Deploy Data Deduplication", Hyper-V Host is in the "Not good candidates for deduplication" list for some reason:

    http://technet.microsoft.com/en-us/library/hh831700.aspx


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    Monday, October 28, 2013 2:16 PM
    Moderator
  • Hi,

    Thank you for posting your question. This is indeed very interesting. There are no limitations for deduplicating volumes with turned off VM’s VHD/VHDX files. Live file support for dedup is only limited to VDI. Even if this would be somehow caused by dedup alone I would still understand any form of corruption, but files disappearing is very strange. One could turn on audit on the files; I would rather suspect an interfering driver able to interact on the IO stack. This could be anything installed from antivirus software to any backup solution, encryption software or basically any driver loaded.

    Thanks,
    Basar

    Monday, October 28, 2013 3:23 PM