[systemd-bugs] [Bug 78337] journald can be very slow (on btrfs ?)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=78337

--- Comment #6 from Lennart Poettering <lennart at poettering.net> ---
(In reply to Radek Podgorny from comment #5)
> ok, nice! but is it safe? wouldn't the journal be damaged on sudden power
> failure, then? (and logs are usually the most important thing to have when
> anything goes wrong)

With the NOCOW flag set data integrity guarantees on btrfs degrade to the same
ones made by ext3/4 which should be pretty much OK. Also, the journal does its
own checksumming, and hence should be capable of detecting corruptions (though
not fixing them). Given that we have a "mostly append + update ptrs at front"
write pattern the expected data loss if some writes are missing or written in
the wrong order should be limited: either the pointers are missing but the
appended data written, in which case the appended data will simply not be
considered but everything else is OK. Or the data is missing and the pointers
set up, for which case we have careful checks in place. 

All in all I think we should be OK.

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