migrating from dovecot to cyrus

[Murray Trainer]

On Tue, 2006-06-27 at 14:49 +0200, Marten Lehmann wrote:
> Hello,
> 
> > Just out of curiosity, what kind of performance problems at what load do 
> > you have. It was claimed that dovecot is really fast and we plan to 
> > evaluate it in the near future for some projects so any hints where to 
> > dig are welcome.
> 
> the difference is, that cyrus handles a lot of things while the mail is 
> being delivered, which saves a lot of time. We had to split the incoming 
> mailserver (smtp) and the pop3/imap server because one server couldn't 
> handle the load any longer.
> 
> Example delivery with exim+dovecot:
> To check the quota, exim has to count all messages (files) in all 
> directories in the maildir (very timeconsuming with NFS mounted maildirs).
> Then the message is delivered to maildir/tmp and moved to maildir/new 
> (another two NFS operations).
> When a user is connecting to IMAP now, dovecot has to look through all 
> directories within the maildir of files or gone, new ones appeared and 
> build the cache and index accordingly. This is done locally on the disk, 
> so it is a bit faster, but it is time consuming on big maildirs anyway.
> Now dovecot can start serving the new message.
> 
> Example delivery with exim+cyrus:
> Exim sends to message to cyrus via unix socket or tcp socket. The rest 
> is done locally on the cyrus backend server:
> Checking for quota
> Updating indizes
> Possibly notifying an existing imap-connection about the new message
> So the delivery is very fast, because cyrus doesn't have to look through 
> all messages to check the quota: It can be looked up in the index.
> When the user is connecting to IMAP, the index is already prepared, 
> cyrus doesn't have to look for changes in the maildir at this stage so 
> it can serve the new message immediately.
> 
> In small setups with everything on one server, exim (or any other mta) + 
> dovecot should work fine, while cyrus is maybe a bit more complicated to 
> setup. But with bigger setups (or expected growth in the future) cyrus 
> and its option of cyrus murder should scale better.
> 
> Regards
> Marten

Although the comparison below includes a commercial imap server, it does
give a good comparison between Cyrus and other open source imap servers.

http://www.isode.com/whitepapers/mbox-benchmark.html

Murray