Re: Why so much "btrfs send" data for "cp -a --reflink"?

[Torsten Bronger <bronger@physik.rwth-aachen.de>]

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Hallöchen!

Torsten Bronger writes:

> I have two subvolumes A and B.  „A“ contains 50GB data, B is empty.
> None is a snapshot of the other.  Now, I copy all data from A to B
> with "cp -a --reflink A/* B".  This copying takes less than a
> second.  So apparently, no bulk data was duplicated.  "diff -rq A B"
> is empty.  So far, so good.
>
> However, it surprises me that
>
>     btrfs send -p A B | wc -c
>
> reports 12GB.

At <https://wilson.bronger.org/btrfs-receive.dump.xz>, I have
uploaded the output of "btrfs receive --dump".  Apparently, there
are many "write".  Why doesn’t btrfs detect that all those extents
are present in the parent?

Regards,
Torsten.

-- 
Torsten Bronger

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