Subject: mailbox formats, system load etc.

From: Andrew Daviel <[email-masked]>
Date: Wed, 27 Sep 2000 12:52:52 -0700 (PDT)

We have a Linux server running the imap-4.7 imapd and popd, with
about 600 users. About 100 have more than 1MB inbox, about 30
more than 10MB, 1 more than 100MB (histogram looks a bit like
y=300M/x). Some users are using POP3, but most are using
IMAP from Netscape which is what we have been 
recommending. We have been migrating people off VMS mail
and POP servers on VMS and there's still a few left so
things will get busier still, and of course more people are sending 
big attachments - 50MB or larger (legitimate) images. Most of our
users are on 10bT or 100bT Ethernet and are always on, so they
may have an imapd running for long periods of time - there are 96
at the moment. imapd for the heavy users seems to run about 5MB
with 3MB resident (RSS)

I'm looking for ways to improve the speed. The machine is
a 350MHz Pentium II with 128Mb RAM and a SCSI RAID array.
I have converted the folders to mbx format (according to Mark,
"This is the current preferred mailbox format. It can be
handled quite efficiently ..") thinking that it would allow
faster message seeking etc., but I'm not so sure this
is really the case.

Persuading people to move mail to other folders would help,
though if they have client-side filtering it can only
take effect when they connect. We don't allow general access so
server-side filtering is a problem.

I guess more RAM or CPU might help, but I was wondering if anyone had
any configuration hints.

Andrew Daviel, TRIUMF, Canada
Tel. +1 (604) 222-7376
[email-masked]
PGP ID 0xC7624B49

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From: Malcolm Beattie <[email-masked]>
Date: Thu, 5 Oct 2000 21:01:20 +0100

Andrew Daviel writes:
> recommending.
[...]
> faster message seeking etc., but I'm not so sure this

As part of our mail cluster, we have two different 350MHz Pentium II
with 512MB RAM each (memory is cheap), each with 4300 users and
performance is fine--there'll be more users on each machine as time
goes by. Quotas are 20MB for undergraduates, 50MB for others (I'm not
sure of the proportion of each off the top of my head). We use mbx
format and most access is IMAP but, as usual, there are still some
POP diehards. These two nodes each have a couple of fast-wide SCSI
buses (old) with a 6x18GB bus and a 6x9GB bus, mirrored in pairs. If
you mail me (off-list is probably best) with more information on the
I/O configuration, kernel version, passwd configuration and so on of
your system, I'll try to help fix up what the glitch is.

--Malcolm

-- 
Malcolm Beattie <[email-masked]>
Unix Systems Programmer
Oxford University Computing Services