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I would like to have one storage pool with multiple disks. Raid5 for metadata of course. But for user-data I would like to set the level of redundancy on a per file or per subvolume level. Can BTRFS do this?

In ZFS there is a 'copies' attribute that is supposed to have this effect. The BTRFS wiki page lists the feature "File Mirroring". But does that refer to full data mirroring or actually on a per file basis?

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    “Raid5 for metadata of course.” – Metadata is important and relatively small. It would have a very high importance/size ratio so wouldn't you want RAID 1 for metadata?
    – James Haigh
    Mar 19, 2015 at 10:06

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The per-file mirroring feature doesn't appear to be implemented yet.

If everything is RAID-1 (or RAID-0, or in general all the same RAID level), then yes, we could give a sane and consistent value from df. However, we have plans to allow per-subvolume and per-file RAID levels. In this case, it becomes impossible to give a sensible estimate as to how much space there is left.

If you need this functionality now, ZFS on Linux is very stable (and probably a better bet in terms of completed features and mindshare).

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