On Wed, Jan 7, 2015 at 1:10 PM, Josef Bacik <jba...@fb.com> wrote: > On 01/07/2015 12:43 PM, Lennart Poettering wrote: >> >> Heya! >> >> Currently, systemd-journald's disk access patterns (appending to the >> end of files, then updating a few pointers in the front) result in >> awfully fragmented journal files on btrfs, which has a pretty >> negative effect on performance when accessing them. >> > > I've been wondering if mount -o autodefrag would deal with this problem but > I haven't had the chance to look into it.
I've been using autodefrag and haven't run into journal corruptions that I can attribute to btrfs since the last one was fixed over a year ago. Chris Mason has suggested preference to use of autodefrag for this use case rather than xattr +C. But I don't know the time frame for autodefrag by default, it's come up a couple times but it's not the default yet. I've found autodefrag journals are less than 200 fragments, and average between 50-150 fragments. Without it, this spirals into thousands quite quickly. Searches don't seem slower when journal files are made of a few extents vs ~ 100, but beyond several hundred let alone several thousand it becomes noticeable. A somewhat minor negative of +C: In case of RAID 1 or higher and silent data corruption, there will be no Btrfs detection due to lack of checksum and therefore no correction. In the case a drive reports a read error then it's corrected, same as with md or lvm raid1+. -- Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
