[Dovecot] Question about "slow" storage but fast cpus, plenty of ram and dovecot

Hello

We are using dovecot 1.2.x. In our setup we will have 1200 concurrent imap users (maildirs) and we have 2xraid5 sas 15k diks mounted by iSCSI. The dovecot server (RHEL 5 x64) is

a virtual machine in our vmware esx cluster. We want to minimize disk I/O, what config options should we use. We can "exchange" CPU & RAM to minimize disk i/o.

Should we change to dovecot 2.0? Maybe mdbox can help us? Maybe ext4 instead of ext3? Any idea is welcome.

Regards

Javier