[Dovecot] issues migration from dovecot 1.2 to version 2

[Rajesh M]

hi

my system is a centos 5 with qmailtoaster

i migrated my email server with around 5000 users from dovecot version 1.2
to version 2

i have two separate 2 tb hdd's storing webmail data of these users.

the load on the server goes very high over 100 during peak load times and
the imap connections get dropped frequently, webmail becomes very slow.

however pop3 download works ok

in the dovecot log file i get errors as such

Warning: Maildir /homebackup/domains/xxxx/xxxx/Maildir/.ALL_INBOX MAIL:
Synchronization took 71 seconds (20 new msgs, 0 flag change attempts, 0
expunge attempts)

i had configured dovecot 1.2 using source
but i had installed version 2 using qmailtoaster rpm

i am a bit confused as to what settings are to be done for a very busy server

note that the cpu system usage and ram usage are less but IO wait goes to
around 80-90 percent

can you please guide me or post some dovecot version 2 config file
settings that are relevant to a busy server.

rajesh