out-of-band dedup status?

[Christoph Anton Mitterer <calestyo@scientia.net>]

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Hey.

I just wondered whether out-of-band/"offline" dedup is safe for general
use... https://btrfs.wiki.kernel.org/index.php/Status kinda implies so
(it tells about unspecified performance issues), but this seems again
already outdated (kernel 4.7)...
:-(

My intention was to use it with duperemove, but AFAIU, the kernel
itself will anyway do a byte-by-byte comparison before any
deduplication, so in principle it should be totally safe regardless of
the stability of the userland tool, right?
Especially I wouldn't want that "identity" is only assumed because of
some checksum identity (or collision ;) ).

Also, is there anything to take note of when this is used with
compression and snapshots?

What when I use it with incremental send/receive... i.e. I dedupe the
"master" and then send/receive this to another btrfs... will it work
(that is will the copy be also deduplicated, with no longer needed
extents properly being freed)... or at least not cause any corruptions?

Any other things in terms of possible issues, data corruption, etc.
that one should know when using deduplication?


Thanks :)

Chris.

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