I'm not a postfix expert, however, if it's like any other MTA it's "queue" directory is usually what runs pretty hot. The first thing I would do is isolate the MTA-related stuff to a very fast piece disk that is *not* the same storage that houses you Cyrus mailboxes & databases.
The second thing to consider is that the performance on modern SATA drives, if you're using a driver for the SATA interface that supports advanced features such as command queueing, are going to show you performance akin to SCSI drives -- even more so if you place them behind a 'quality' RAID subsystem that provides read/write caching.
But, if you're really getting your system to buckle under I/O load, the first thing you should consider doing is split out the functions. The first thing I would do is migrate the MTA (postfix) duties to some other systems (plural, because you should never have just one of anything) and deliver to your Cyrus install via LMTP over TCP. From there, you'll be able to scale each to those subsystems appropriately, without worry that one's I/O load profile is directly impacting the other.
-rob ---- Cyrus Home Page: http://asg.web.cmu.edu/cyrus Cyrus Wiki/FAQ: http://cyruswiki.andrew.cmu.edu List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
