From: Torsten Bronger <bronger@physik.rwth-aachen.de>
To: linux-btrfs@vger.kernel.org
Subject: Why is "btrfs send" large after "cp --reflink"?
Date: Tue, 22 Dec 2020 14:23:43 +0100 [thread overview]
Message-ID: <87czz2ug80.fsf@physik.rwth-aachen.de> (raw)
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Hallöchen!
1. I have a subvolume "VirtualBox" with an OS image (50 GiB VDI file).
2. I create a read-only snapshot with "btrfs su sn -r VirtualBox
parent".
3. I work with the OS, changing some data within the VDI file.
4. "btrfs p s VirtualBox ro true"
5. "btrfs send -p parent VirtualBox | wc -c" yields 60 MiB.
6. "btrfs su c temp"
7. "cp -a --reflink VirtualBox/* temp"
(takes less than 1 sec)
8. "btrfs send -p parent temp | wc -c" yields 12 GiB.
Why does "cp --reflink" break so much that the size of "btrfs send"
jumps from almost nothing to one quarter of the whole subvolume
size?
Regards,
Torsten.
--
Torsten Bronger
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reply other threads:[~2020-12-22 13:31 UTC|newest]
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