The first thing that you should do is update your software. imap-2002d is
an older version. The current release version is imap-2004e.
In traditional UNIX mailbox format, it is necessary to read every byte of
the file as part of startup. A 200MB mailbox is a lot to read. It may
also be necessary to do some rewriting to assign UIDs and status to
newly-delivered messages. I agree though that your 540MB disk cache
should keep this from happening.
One step to do if you consistantly have a mailbox of that size is to
switch to the mbx format. It greatly reduces the number of reads when the
mailbox is opened, as well as the number of writes to update the mailbox.
To get started on mbx format, read the following FAQ:
http://www.washington.edu/imap/IMAP-FAQs/index.html#4.5
Next, you need to investigate if the I/O wait isn't due to something else.
For example:
(1) imapd does a reverse DNS lookup on the client's IP address to get its
name.
(2) the c-client library attempts to launch IMAP-via-rsh to avoid the
need to negotiate authentication. Unfortunately, rsh tends to block
for a minute if the rsh attempt is refused rather than quit
immediately.
If either of these are the problem, it will show up even with small
mailboxes.
Finally, does the problem happen with an IMAP client such as Pine? I
don't know whether squirrelmail does this, but many webmail programs
literally make a separate IMAP connection on a per-click basis. This puts
a tremendous I/O load on the IMAP server. Only a few very well-written
webmail programs maintain a static IMAP connection in webmail.
-- Mark --
http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
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