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