Chris,
-----Original Message----- Subject: Re: [Dovecot] Significant performance problems
Try bumping up the RAM on both servers to 8+GB, and make sure that you don't have any mount options that would prevent the client from caching data - noac for example is a killer. You could also try mounting with noac, and disabling or turning down speculative readahead on the NFS server.
Sorry - don't try noac, try noatime! Big difference!
As an additional data point, I will say that we see Dovecot processes for 900 concurrent users consume about 3GB of memory. If your system is anything like ours, you've probably got less than 1GB of memory left for the kernel to use as filesystem cache. Throw as much memory as you can spare at the Dovecot and NFS servers, and see what happens.
-Brad