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Thick / Thin and UNMAP

    Question

  • Hi

    We're running 2012R2 (moving to 2016 soon) and experiencing some issues with UNMAP. We already discovered that with deleting large files on thin disks on thin LUNs, we see a freeze of the VM for a few seconds. Disabling UNMAP inside the VM or provisioning the VHDX as thick, will solve the issue.

    But one question remains, which we can't test right now because of time constraints, will a thin VHDX on thick CSV also trigger UNMAP? 

    Can anyone maybe answer this?

    Gabrie

    Tuesday, January 8, 2019 6:15 PM

Answers

  • Hi,

    Based on my research, Windows cannot know if the storage is support for this and will not stop UNMAP automatically.

    You could disable it by manually.

    Best Regards,

    Frank



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    • Marked as answer by Gabrie Thursday, January 10, 2019 10:22 AM
    Thursday, January 10, 2019 7:57 AM
    Moderator

All replies

  • Hi,

    It is supported regardless of fixed or dynamic if your hardware storage support.

    It is enabled by default.

    I suggest you consult your storage vendor for better answer.

    Best Regards,

    Frank


    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    Wednesday, January 9, 2019 9:38 AM
    Moderator
  • Hi,

    Thank you for your answer. I doubt however my storage vendor is able to answer how VHDX files work.

    If my storage array offers a thick LUN, the thick LUN will not perform UNMAP. My question is, will Windows know about this and stop giving UNMAP commands through the VHDX to the array or will Windows detect UNMAP is no longer active on the LUN (Array) and not try to perform UNMAP?

    Gabrie

    Wednesday, January 9, 2019 10:30 PM
  • Hi,

    Based on my research, Windows cannot know if the storage is support for this and will not stop UNMAP automatically.

    You could disable it by manually.

    Best Regards,

    Frank



    Please remember to mark the replies as an answers if they help.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com

    • Marked as answer by Gabrie Thursday, January 10, 2019 10:22 AM
    Thursday, January 10, 2019 7:57 AM
    Moderator