2009-01-12 12:47:57

by Alex Buell

[permalink] [raw]
Subject: Fw: Online ext4 defragmention

On Sun, 11 Jan 2009 15:28:38 -0500, I waved a wand and this message
magically appears in front of Theodore Tso:

> On Sun, Jan 11, 2009 at 01:44:43PM +0000, Alex Buell wrote:
> > Can someone confirm if the online ext4 defragmentation ioctls will
> > be going into 2.6.29? Thanks, I'm planning a migration from a
> > disparate collection of filesystems to ext4 over the next few
> > months.
>
> Unfortunately, the defragmentation patches need to a lot of work (to
> be honest, largely refactored and almost rewritten) before they are
> ready to for mainline yes. I am also concerned that the current
> defrag patches also try too hard to keep blocks in the same block
> group, even as a higher priority keeping them non-fragmented.

So maybe 2.6.30? :-D

> Also, note that some of the benefits of ext4 only show up if you do a
> backup, mkfs, and restore; that's because there are layout changes
> that can only take place if you reformat the filesystem. Finally,
> there are some allocation algorithm changes which didn't make the
> 2.6.29 merge window which I think will make a long-term difference.
> So you'll probably want to use 2.6.29 with the ext4 patch set.
>
> So if you want the best performance and fastest fsck times (which I
> infer given your query about the defragmentation ioctls), you may want
> to consider doing a reformat and restore operation as part of your
> ext4 migration, at least for filesystem that you plan to use for
> active use. If the filesystem is just going to be an mp3 archive, for
> example, it might not be worth it to do the backup/reformat/restore
> path.

Having done 1) remounting ext3 volumes as ext4 and 2) backing up data
before reformatting as an ext4 volume, and restoring afterwards, and
noticed that with option 2 I got noticeable improvements in
performance.

Thank you for your advice, it seems reformatting is the best thing to
do.
--
http://www.munted.org.uk

Fearsome grindings.


--
http://www.munted.org.uk

Fearsome grindings.