[Dovecot] Questions about converting maildir to mdbox.

Stan Hoeppner stan at hardwarefreak.com
Sun Apr 10 23:54:13 EEST 2011

Henrique Fernandes put forth on 4/10/2011 12:29 PM:

> We are using dovecot 2.0.6 with maildir in an ocfs2 partiton.
> It is pretty slow access in peak time, but it is related to ocfs2 as i said
> before, i am trying to mimimize the ocfs2 latancy by using mdbox. Another
> problem that we have are Full backup that takes about 24h and incremental
> takes about 13h

Last you posted here you didn't have enough spindles in the array for
the size of the workload, and you didn't have a dedicated quality GbE
switch for strictly OCFS traffic between Dovecot hosts.  Has any of this
been rectified?  If not, changing mailbox formats isn't going to fix
your problems.  If you really want to test this theory to the limit,
converting to mbox (yes, good old mbox, without the d) will reduce
metadata load more than mdbox, by a huge margin.

Given the constraints on your ability to reconfigure the disks in the
EMC array (as someone else owns it and you're borrowing space) to meet
your needs, and your apparent lack of funding allowing purchasing your
own array, the things you should really do to fix most of your problems are:

1.  Stick with maildir
2.  Configure a Dovecot director box to achieve stickiness
3.  Put a quality 200GB SSD drive in each Dovecot IMAP server
    (smaller if you can get away with it to save $$, larger if
     if 200GB isn't enough)
4.  Change the index location on each server to the local SSD drive

Over time the user indexes will be gradually rebuilt onto the local fast
SSD drive.  This will eliminate the bulk of the IOPS load on OCFS, and
should fix your performance issues pretty thoroughly.  Well, except for
the slow backup.  The only way around that is more spindles in the EMC
array LUN where mailboxes reside.


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