Yesterday finally saw the deployment of the new IMAP server, and there was much rejoicing. Feedback from users ranged from "definite visible performance improvements" to "holy dogshit this new server is fast." Hopefully it'll continue to be fast. A big part of what slowed down the old system was the multiple I/O intensive tasks running simultaneously, and we haven't seen that happen on the new hardware yet. There are two main tasks that run periodically and really hit the disks hard. The first is the filesystem backup, which stats every file on the system and reads a whole bunch of them. The second is the server side search index generator, called squatter, which does something fairly similar in order to build indexes of message comments so fast server-side searches can be performed. Think of this as somewhat similar to the Unix updatedb/locate commands, except that it indexes files by content. More like Google Desktop, I guess.
One thing that makes me somewhat optimistic, though, is that I manually triggered a squatter run against a subset of our mailbox list, and it took 2.5 hours on the new hardware. Looking at the most recent two automated runs over the same set of folders on the old hardware shows that they each took well over 13 hours! That's a huge difference! I don't know if the backup process was running at the time or not, but I suspect it was. It wasn't when I triggered the manual run. Either way, we should probably work out a way to avoid having backups and squatter run at the same time. That's somewhat difficult, though, since backups could take several days on the old hardware. Hopefully the newer system really is faster!
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