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Windows server 2012 with deduplication show wrong "size on disk" RRS feed

  • Question

  • Running 2012 server with deduplicated volume (performed by windows server).

    Volumesize is 5 TB, free space is 2,2 TB, reported Dedupliction rate is 47%. This I believe is correct.

    However the properties for the only folder on the drive reports:

    Size:              5,31 TB (5.848.049.807.909 bytes)
    Size on disk:  90,7 GB (97.404.194.816 bytes)
    Contains:       1.215.797 Files, 52.169 Folders

    There are only one folder in the root of the volume, why it’s not just files that already resides in other folders on the volume.

    Individual folders shows correct values just after they are copied to the volume, but after deduplication is run (and the retention period for the files has passed), Size on disk shows as very small.

    The behavior can be reproduced on a other volume.

    Kind regards

    Knud E. Jensen

    Thursday, June 13, 2013 5:52 AM

Answers

  • Hi,

    If there is only 1 folder listed in root of the volume, I assume the "System Volume Information" folder is not displayed as by default it is hidden. 

    With Deduplication started, duplicated files are actually moved to that folder, and the original file is replaced by a junction point. Thus the Size on disk is low because junction point is almost no size. Meanwhile as we do not have permission on System Volume Information folder (and it is hidden in your case), the total size by select all folders are not calculated by right click and choose Properties.


    TechNet Subscriber Support in forum |If you have any feedback on our support, please contact tnmff@microsoft.com.

    Friday, June 14, 2013 2:36 PM

All replies

  • Hi,

    If there is only 1 folder listed in root of the volume, I assume the "System Volume Information" folder is not displayed as by default it is hidden. 

    With Deduplication started, duplicated files are actually moved to that folder, and the original file is replaced by a junction point. Thus the Size on disk is low because junction point is almost no size. Meanwhile as we do not have permission on System Volume Information folder (and it is hidden in your case), the total size by select all folders are not calculated by right click and choose Properties.


    TechNet Subscriber Support in forum |If you have any feedback on our support, please contact tnmff@microsoft.com.

    Friday, June 14, 2013 2:36 PM
  • Sorry for necroing this thread, but i've seen more people give the wrong answer around the web than simply answering the question.

    Yes, this is obtusely hidden from the user interface and microsoft has gone so far as to outright lie in the demo videos when launching the feature (check them out, they are still at channel9, from the build conference last year), where a microsoft representative happily goes on with something to the effect of "see? here are virtual machines with vhd's deduped, and now they take only a few KB of disk" by going into preferences and showing the size. Thats a glaring lie.

    This is how you check the size of a deduped folder or path:(powershell, no ui)

    measure-dedupfilemetadata <path>

    It will tell you effectively how much space the path is taking, how much is actually deduped and how much info is unique. That is what the ui should report when you check the size through properties on a deduped location, and nowhere are you told this.

    Hope this helps someone still fighting to get this information.

    • Proposed as answer by Setsunaaa Monday, December 22, 2014 11:37 PM
    Monday, May 26, 2014 4:32 PM
  • With Deduplication started, duplicated files are actually moved to that folder, and the original file is replaced by a junction point.

    This is SO wrong, how can a Microsoft moderator give such wrong answers?

    It is not the "deduplicated file" which is moved, the deduplicated parts of the file are moved. Take two files, 50 % identical, then only the 50% are deduped, and the rest not. So the explorer only shows the non-deduplicated part as "in use", while the deduplicated part is simply not counted since the explorer ask for "used blocks" instead of counting up the file size.

    A Junction or Hardlink are different approaches to save space. Windows 7 heavily uses hardlinks for it's Windows directory to save space, i.e. a file (the complete file, not just a part of it) is stored only once, and referenced from multiple locations.


    • Edited by Setsunaaa Monday, December 22, 2014 11:28 PM
    Monday, December 22, 2014 11:20 PM