[systemd-devel] [ANNOUNCE] systemd 219

[Lennart Poettering]

On Tue, 17.02.15 20:05, Goffredo Baroncelli (kreijack at libero.it) wrote:

> Hi Lennart,
> 
> On 2015-02-16 23:59, Lennart Poettering wrote:
> >         * 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.
> 
> If I read correctly the code, the FS_NOCOW is a temporary workaround, i.e.
> when the file is closed (or rotated ?) the FS_NOCOW flags is unset again. 
> It is true ?

Well, we try to unset it, but this is not allowed by btrfs. However,
given that it might be allowed one day, we do it anyway.

In effect this means FS_NOCOW is set for good once we turn it on.

Lennart

-- 
Lennart Poettering, Red Hat