[systemd-devel] [PATCH] Set the NOCOW flag for the journal via tmpfiles

Goffredo Baroncelli kreijack at libero.it
Sat Mar 21 04:56:51 PDT 2015

Hi all,

these patches set reverts the commit 11689d2 "journald: turn off COW for
journal files on btrfs" which enables *unconditionally* the NOCOW flag for the
journal files. The reason was that the performances of the journal file format
are very bad on btrfs, and decrease during the time. Disabling the COW
behavior, the perfomances increase.
Unfortunately disabling the COW behavior leads to disable the BTRFS checksums,
which in turn prevents BTRFS to rebuild a corrupted file in a RAID
filesystem [3].

To avoid that I proposed a patch which introduces a configurable option to
disables the "turn off COW" behavior[1]. Lennart commented that instead he
prefer to set the NOCOW attribute via tmpfile.d snippets.

A further patches set was proposed and accepted [2] to extend systemd-tmpfiles
to change the file attributes.

This last patches set removes the "turn off COW" behavior (patch #1) and
introduces a new tmpfiles.d snippet which enable the NOCOW beahvior for the
journal files (patch #2). So a sysadmin can disable this setting overriding
this file configuration.


[1] Re: [systemd-devel] [RFC][PATCH] Add option to enable COW for journal file

[2] https://www.mail-archive.com/systemd-devel@lists.freedesktop.org/msg29313.html

[3] http://en.wikipedia.org/wiki/Btrfs#Checksum_tree_and_scrubbing

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