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I have enabled data deduplication on one of my SSD's volumes and then run Start-DedupJob cmdlet with optimizastion parameter on this volume (Windows Server 2012). After dedup completed i check Get-Dedupstatus and get this output:

FreeSpace    SavedSpace   OptimizedFiles     InPolicyFiles      Volume
---------    ----------   --------------     -------------      ------
81.25 GB     9.44 GB      2                  11                 D:

Howevere when i have checked disk space, i discovered that free space was not increased, but instead decreased. (I had 88Gb of free space before deduplication, and after i had 81.25Gb of free space). Also I have checked the only folder in this volume and found it has the same size as before dedup.

Also i tried Start-dedupJob with GarbageCollection type after all, and now i have that output:

FreeSpace    SavedSpace   OptimizedFiles     InPolicyFiles      Volume
---------    ----------   --------------     -------------      ------
81.26 GB     0 B          2                  11                 D:

Why data deduplication worked so strange for me?

ko4evneg
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  • Sure folder size will not go down. Dedup is transparent to the user. A 100gb file is a 100gb file - whether it is deduped or not, the FILE is 100gb always in size. Dedup will not show a smaller file. – TomTom Dec 15 '13 at 10:28
  • Can you say more about the folder? "the only folder", 2 files optimized, 11 in policy - does not sound like a good use case for dedupe. – TomTom Dec 15 '13 at 10:29
  • In this folder I have 11 VHDs with virtual machines. So i thought it's a good idea to dedup them, as windows deduplication is block-level – ko4evneg Dec 15 '13 at 10:30
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    Yes, that then makes sense. 11 vhd's should have plenty of identical blocks. Assuming they are old enough.... (and not active / open - open files are not deduped). Deduping active VHD's is only supported in 2012 R2 on a VERY spceific scenario (hyper-v on separate server). – TomTom Dec 15 '13 at 10:58
  • Okay. So i think that's the cause. I tried to dedup active VHDs, just configuring the setting to dedup file older than 0 days. – ko4evneg Dec 15 '13 at 19:05
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    Wopn't work. You are in not supported territory. Active VHD dedupe is a 2012 R feature on a SEPARATE FILE SERVER ONLY - not on the Hyper-V machine itself. – TomTom Dec 16 '13 at 06:58

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