We are in desperate need of a new e-mail server solution and would
like to get opinions and real world benchmarks of what others are
using.
Here is our current setup and problems:
New Intel Xeon Xserve 4GB RAM, OS X Server (was 10.4.10 now 10.5)
using OSXS built-in mail, mail store is on connected Xserve RAID
(RAID 5).
There are 650 active mail accounts, with anywhere from 200-350
users being connected at once, (at least trying).
All accounts are IMAP.
We have set up Shared folders, also.
Users do not have mail quotas.
All users are in Open Directory. The mail server is also a replica
of the OD.
The problem we are having is the server can not handle this load.
We have worked for months with Apple and have not been able to make
things better. At peak times the server comes to a crawl, so much
so that mail connections time out etc.
My first guess is that you don't have enough RAM. Looking at my
server it seems that each IMAP connection is using about 3MB of RAM.
If I were being conservative I would say 4. Each of my clients looks
to have 2 connections open to the server, sometimes they launch more
when starting up. If you said 350 users were connected at once, that
would be 700 connections. If you allowed for three connections per
client to be safe, that would be 1050 connections at 4MB each which
would work out to over 4GB of RAM.
Another possibility is that the XServe RAID is not handling the tons
of small reads and writes that occur very well. I would normally try
to go with SCSI disks for this type of situation, but you didn't
really say what kind of troubleshooting you've done to figure out
where the problem is.
If you are running low on RAM, you can tell this pretty easily by
using top in the terminal. Just leave a terminal window open and run
top in it. When you start having the massive slowdown, look at the
pageouts. If it's increasing, that means you've run out of RAM and
the OS is compensating by using disk. That will easily cause the
symptoms you're seeing.
HTH,
Kevin
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