[systemd-devel] [PATCH V2] Set the NOCOW flag for the journal via the tmpfiles

[Goffredo Baroncelli]

Hi all,

these patches set partially 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.

BR
G.Baroncelli

Changelog:
v1: first issue
v2: revert only the part related to SETTING the NOCOW attribute of the
    commit 11689d2
    update the comment in the "tmpfile snippet"


[1] Re: [systemd-devel] [RFC][PATCH] Add option to enable COW for journal file
https://www.mail-archive.com/systemd-devel@lists.freedesktop.org/msg28724.html

[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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