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Re: [Xen-users] mail server on a xen guest?

To: Nico Kadel-Garcia <nkadel@xxxxxxxxx>
Subject: Re: [Xen-users] mail server on a xen guest?
From: John Haxby <john.haxby@xxxxxxxxxx>
Date: Tue, 08 Jul 2008 12:58:25 +0100
Cc: Peter Peltonen <peter.peltonen@xxxxxxxxx>, Xen-users@xxxxxxxxxxxxxxxxxxx
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Nico Kadel-Garcia wrote:
Peter Peltonen wrote:
I'm building a new qmail based mail server. I now have a quad-core
*WHY*??? Qmail has many cool technical features, but it's licensing has been extremely burdensome, as has its packaging. Mr. Bernstein has relented and placed his work in the public domain, but it languished for years for that reason. Debugging it in any environment without your own sophisticated sys-geek to work around Mr. Bernstein's policies is.... awkward.

I agree completely with this -- qmail is a pain and there are good reasons why it's not in the major distros.

server with 8 gigabytes of RAM and RAID-5 disk setup. I need to run a
virtual web server on that host too, so I'm installing Xen on that
host.  What I am wondering now is should I install qmail also on a
virtual server (domU) or on the master server (dom0)? Has anyone
experience about running qmail under xen domU? I could dedicate 1-2
cores for the qmailtoaster domU and lots of RAM, but I'm a bit worried
about disk I/O, as I've read that this can be a bottleneck in Xen. I'd
like to hear stories like "I've run mail server on a domU with 100
active domains and 10 000 incoming messages a day without problems)"
Why not use Dovecot? It's built into contemporary Fedora and CentOS, which themselves are well integrated with Xen and perform reasonably well in paravirtualization.

And you can use MRTG and tools like it to monitor your disk I/O now, to get some sort of standard to compare against.

RAID5 isn't going to be good for mail: a lot of the disk-writes are going to be very small and there are going to be a hell of a lot of them, especially with that kind of incoming load. Actually, with that kind of incoming load I don't think you're going to want to run the mail server on anything other than the bare metal anyway: virtual machines work well when you have servers that are individually relatively lightly loaded and it doesn't look as though yours is.


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