[Dovecot] Disk busy issues

[Michael Durket]

I have a system with currently 121 mail accounts running Dovecot  
1.1.20 on Redhat AS4.
The computer has 8 gigabytes of memory, 2 dual core AMD Opteron  
processors and is
attached via fiber channel connections to 345 gigabytes of space for  
the home directories.

The only purpose for this machine is as an IMAP server and yet several  
times throughout
the day the disk utilization on the home directories goes to 100% for  
significant periods
of time. I'm using Dovecot because of its reliability and message  
indexing features, and I
would expect this system to be way more than what's needed for the  
job, but the disk busy
issues bother me, especially with this small number of users.

I'm wondering if the problem here is that all the mailboxes for these  
users are in mbox
format and that format just poses too much of a burden on Dovecot. I  
personally as an
experiment have been using Maildir format and that seems to work fine.  
Would people
on this forum (who probably deal with larger numbers of users and  
mailboxes than my
system does) recommend that I switch the mailboxes over to Maildir  
format to alleviate
the disk busy problems? Are there any issues to watch out for when  
converting mailboxes
from mbox to Maildir format?