[Dovecot] Dovecot performance on GFS clustered filesystem

[Allen Belletti]

Hello All,

We are using Dovecot 1.1.3 to serve IMAP on a pair of clustered Postfix
servers which share a fiber array via the GFS clustered filesystem.
This all works very well for the most part, with the exception that
certain operations are so inefficient on GFS that they generate
significant I/O load and hurt performance.  We are using the Maildir
format on disk.  We're also using Dovecot's deliver from Postfix to
handle local delivery.

As best I can determine, the worst problems occur when certain users
with very large Inboxes (~10k messages) receive new mail and their
client looks up information about that message.  GFS doesn't seem to
efficiently handle the large directories that contain folders like
this.  As a result, lots of I/O ops are generated and performance
suffers for everyone.

I am beginning to wonder if it might be more efficient to revert to the
old mbox format, with one file per folder (plus whatever indices are
creates.)  It seems that this ought to work better with GFS which is
geared toward smaller numbers of larger files.  Is anyone on the list
currently doing that?  Alternately, any thoughts regarding tuning or
other options would be appreciated.

Thanks,
Allen

-- 
Allen Belletti
allen at isye.gatech.edu                             404-894-6221 Phone
Industrial and Systems Engineering                404-385-2988 Fax
Georgia Institute of Technology