Systemd 219 now sets the special FS_NOCOW file flag for its journal
files[1]. This unfortunately breaks the ability to repair the journal on
RAID 1/5/6 btrfs volumes, should a bad sector happen to appear there. Is
this something that can be configured for systemd? Is btrfs going to
someday fix the fragmentation problem, making this option reduntant?
[1]
http://lists.freedesktop.org/archives/systemd-devel/2015-February/028447.html
* journald now sets the special FS_NOCOW file flag for its
journal files. This should improve performance on btrfs, by
avoiding heavy fragmentation when journald's write-pattern
is used on COW file systems. It degrades btrfs' data
integrity guarantees for the files to the same levels as for
ext3/ext4 however. This should be OK though as journald does
its own data integrity checks and all its objects are
checksummed on disk. Also, journald should handle btrfs disk
full events a lot more gracefully now, by processing SIGBUS
errors, and not relying on fallocate() anymore.
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