[Dovecot] Recommended FS for Dovecot Maildir

Lorens dovecot.fdop at tagged.lorens.org
Wed May 10 11:02:21 EEST 2006

On Wed, May 10, 2006 at 02:32:40AM +0200, Wouter Van Hemel wrote:
> It's important to note that these filesystems each have their own
> strengths, and performance will depend on many factors such as the size
> and number of files, parallellism, number and type of disks,
> fragmentation, i/o load, possibly even cpu load. Are we talking about a
> relaying mailserver or end-user storage? Do the users move or delete a
> lot of files? Do they rather use imap, or pop3? What other activities run
> on the machine? How do you see the reliability/performance trade-off?
> In real life, things aren't as clean-cut as in most of those generic
> benchmarks, and people tend to attach too much importance to them and
> then usually get into silly flamewars. :)

Agreed, mostly.  I feel that I need to point the only time ever
where I have noted real-life difference between journaling
file-systems during normal operation.

I use an rsync backup scheme that depends heavily on hard links
(googling rsync backup hard link should give you details). A
typical day's backup would consist of maybe a thousand files
spread across a directory tree consisting of some ten thousand
directories and some hundred thousand+ hard links to files
shared between daily backups. I moved the storage from ext3 to
reiser3. I noted that deleting the directory tree representing a
day's backup went from insignificant minutes to tens of minutes,
hundreds of minutes, sometimes up to a thousand-some minutes.

I found benchmarks that seemed to confirm this advantage of
ext3 over reiser3, so I didn't try any tuning. I didn't feel
strongly enough about it to move the server back to ext3, I just
separated the deleting from the backing up so the the one did
not delay the other.

Of course this use is probably not relevant to a server used for
Maildir or mbox, but it's worth noting that while there can be
differences in performance, the usage pattern has to be really
extreme before you see any difference at the application layer.

> > Long ago I used a benchmark program called 'postmark' to
> > test the speed of file creation/deletion operations that
> > are typical in maildir environments.  I haven't been able
> > to find it recently although the last time I mentioned it
> > someone said it was in the debian repositories and available
> > via apt-get.
> I seem to remember to have used it once too, also in a very vague past.

Well, I have a debian machine, so it's easy to check!

% postmark 1.51-3 File system benchmark from NetApp
% Benchmark that's based around small file operations similar to
% those used on large mail servers and news servers.  Has been
% ported to NT so should be good for comparing OSs.
% http://www.netapp.com/tech_library/postmark.html


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