Hi Timo,
You may remember some of my mails, I was having unusual high load issues using pop3 with dovecot over nfs, and unusual being the load on anywhere from 1 to 4 servers would run at 2 to 4 for a week then all of a sudden would spike to 60 and higher (saw 150 once).
I have been banging my head on the wall for the last 1.5 to 2 months since switching from courier to dovecot, the imap has worked great but the pop3 was a problem out the door.
Anyway, I finally tried loading dovecot directly on our raid, all loads across the board dropped to the floor. The single P4 3ghz purrs along at an easy 0.30 load where the 1 to 4 quad core boxes with brand new hardware were loading up to 60 when using nfs.
So, my experience has been that maildir, nfs and dovecot as the pop3 server was unusable. I wasnt really sure this whole time, it seemed odd that a single P4 box using nfs and courier pop3 could handle the entire system load but dovecot with the same and more quad cores fell over was weird.
Anyway, this is totally not meant as a bashing or anything, just information. Im not a C programmer so I really cant offer anything but my input/observations. Maybe the pop3 part of dovecot isnt really given much love or people are mostly just interested in the imap server? Or maybe most people dont use nfs? Totally just assumptions here.
A definite positive here though, after moving dovecot directly to the raid server, wow, our mail TOTALLY hauls ass now. Two of our managers both noticed the huge speed increase. One of them uses pop3 and leave messages on server and has almost 4,000 messages in the inbox on the server, his webmail now loads literally instantly, i click login and count 1 second. That is amazingly fast.
I dont have any hard numbers, but before our upgrades his "feeling" was that he seems to remember it taking up to 30 seconds for webmail to load his mailbox. that is an incredible difference. Our webmail uses imap by the way, so this is probably a combination of moving from nfs and switching from courier to dovecot.
Ok thanks for your great hard work and sorry for the novel size post.