[ILUG] Linux SMP on Xeons

[Lars Hecking]

Colm Buckley writes:
> 
> Hey, folks -
> 
> Just wondering whether anyone has real experience of running Linux on a
> 4- or 8- way Xeon system.  Any gotchas?  Does performance scale well
> with CPUs?  The system in question is likely to be a high-performance
> mail relay, running a carefully-tuned exim...  I'm hoping that, given
> enough CPU and RAM (say 4 Xeons and 4GB), I'll be able to handle
> something like 80,000 emails per hour.

 Mail is I/O bound.

 From a "# of cpus" point of view, probably over-spec. Make sure you have
 a separate, fast disk (goat type) for the spool area, possibly striped
 across several disks (I'm not too familiar with raid and striping, so
 this may be total bull). Local DNS server to minimise DNS network
 traffic. If you're using Linux (which I wouldn't, in this case),
 use ReiserFS for the spool. FreeBSD (don't know how well it does smp)
 ffs with softupdates is fine, too.

 I am unfamiliar with exim. Is it a monolithic program, like sendmail?
 Both qmail and postfix may allow better tuning by adjusting the max.
 number of daemons; which is where "plenty of ram" figures prominently :)

 I have one or two references to papers about scaling sendmail, which
 I will look up tomorrow, when I'm back in the office. The principles
 apply to other MTAs as well.

 Actually, I found them already :)

 "Sendmail Performance Tuning for Large Systems"
 http://www.shub-internet.org/brad/papers/sendmail-tuning/

 "Scaling sendmail"
 http://www.linuxworld.com/linuxworld/lw-1999-09/lw-09-sendmail.html

 There's a lot of interesting stuff (and hard facts) in the postfix-users
 archive (linked off www.postfix.org).