linux-kernel - Fw: Online ext4 defragmention

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Date:	Mon, 12 Jan 2009 12:46:36 +0000
From:	Alex Buell <alex.buell@...ted.org.uk>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
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.
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