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I have a Windows Server 2012 Hyper-V host with VMs on a dedicated RAID-5 volume. One VM is also running Server 2012 and is being used to serve files. The other VMs are smaller and mostly used for temporary testing scenarios.

The main file server VM has two dynamically expanding VHDX files - one for the OS and one for storage. The VHDX being used for storage has quite a few duplicated files on it.

Should I run Server 2012 deduplication on the volume containing the storage VHDX file on the host, or within the file server VM itself? I understand that running it within the VM will not decrease the size of the VHDX file on the host, but my goal is to enable as much storage capacity within the VHDX file itself. I also understand that if I run it on the host, I will have to take the VM offline to do it. Downtime isn't a concern in this instance, just the best way to do this.

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Deduplicating VHD and VHDX files is not supported. You should not dedupe on the Hyper-V host. Dedupe within the guest.

Edit: Note that this has changed a bit since this answer was originally written. In certain configurations relating to VDI, dedupe of VHD/VHDXs is supported: http://blogs.technet.com/b/filecab/archive/2013/07/31/deploying-data-deduplication-for-vdi-storage-in-windows-server-2012-r2.aspx

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  • That being said, it can be done. It's just not supported by Microsoft. kallesplayground.wordpress.com/2013/12/14/…
    – Brain2000
    Oct 26, 2015 at 22:36
  • Sure. You can do whatever you want, but running your production virtualization solution in an unsupported state is about as bad of a decision as you can make.
    – MDMarra
    Oct 26, 2015 at 22:37
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    While I agree with your statement as a whole, you always must test what you are going to push into production, even if it IS supported. Plus take what I said in context, "Microsoft support". As most of us painfully know, whatever Microsoft supports is a joke, and I use their writings as more of a loose set of guidelines than steadfast rules. It's similar to the Promise enclosure hard drive compatibility list. That too is a joke.
    – Brain2000
    Oct 28, 2015 at 17:53
  • Just to update on the answer, I went to a MSFT demo in 2015 and they were showing us the storage space saving by dedupping the hyper-v data store. (but unfortunately I didn't find any best practice from MSFT on that matter yet online)
    – yagmoth555 ♦
    Jan 30, 2017 at 21:04
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This is now supported on Server 2012 R2

https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/dn486808(v=ws.11)

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