As many people have noticed, email performance during our peak usage time (9:50am-10:20am) has been extremely poor. The main reason we believe is that the disk drives our email inboxes are stored on are just not fast enough. Currently we are using a Sun T3 disk array with a 1Gig cache and 9 fibre-channel disk drives. During this time our usage goes through the roof and the disks just can’t keep up with the demand. When the disks are maxed out, we see about 30MB/s of reading from the disks.
In the short term, here are a couple of things we have done to help reduce the load. First, we have cut back the maximum size of a person’s inbox. We have a script that runs each night and if your inbox is more than 50MB, we move the oldest messages out of the inbox until it is down to about 30MB.
Second, we have installed a newer version of imapproxy on our webmail servers. This new version supports an IMAP SELECT cache which should help when reloading the inbox display because it will have the message headers already cached. Another nice feature of this version is that it now supprts encrypted IMAP connections by using TLS. So now your messages and password are being encrypted while they are being transmitted from the mailserver to the webmail server.
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