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There seems to be a lot of chatter about Microsoft adding missing features to ReFS in Windows Server 2019. Is disk compression now available? And if so, does it work in conjunction with data deduplication?

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ReFS does not support compression, but if you use deduplication on a ReFS volume, compression is used - at least according to this page https://docs.microsoft.com/en-us/windows-server/storage/data-deduplication/whats-new

Screenshot: compression annotated on MS page

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  • Interesting, does this compress all files or are you saying that the deduplication is a form of compression? Is there a way to see statistics on a per file basis to confirm not only this, but how it's being applied and so forth (ie, size of file and size on disk)?
    – ylluminate
    Jun 18, 2020 at 6:54
  • @ylluminate I cannot see any statistics on a per-file basis, but if you run the ddpeval.exe tool, it actually estimates your savings with deduplication - both before and after compression. I suspect that when dedup is used, all chunks that go into the dedup store are compressed. I am not sure if that has the effect of 'compressing' /all/ files, but I would suspect that all of your in-policy files will find themselves in the store with compression.
    – fabspro
    Jun 18, 2020 at 8:11
  • @ylluminate I added a link - docs.microsoft.com/en-us/windows-server/storage/…
    – fabspro
    Jun 18, 2020 at 8:11
  • I appreciate your having noted that - I added an image in an edit for future reference. I'm curious, the latter annotated part says "optional compression" so I have to wonder: is there a way to turn it on since it is "optional?"
    – ylluminate
    Jun 19, 2020 at 20:33
  • @ylluminate I cannot find any setting. My imagination says that whenever a file is optimised, the data is stored into chunks which are compressed before being stored. But I would love to see something more concrete get published into the docs. Maybe worth doing an experiment - empty volume, 1000gb file, see how much disk space is used?
    – fabspro
    Jun 21, 2020 at 4:59
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Unfortunately it appears that Microsoft has not yet added compression to ReFS in Windows Server 2019 (version 1709) as per this document:

table

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