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Re: Sendmail or Qmail ? ..

On Thu, 4 Sep 2003 22:58, Eric Sproul wrote:
> First, scale is a consideration.  Once we began to grow our customer
> base, our email volume began to increase dramatically.  Qmail queues
> everything to disk, so the more mail you do, the more pressure you put
> on your disk I/O.  The server running Qmail was always blocking while it

I was under the impression that Sendmail also queues everything to disk.  How 
does it's queue operate then?

> where the mailbox is).  We chose OpenLDAP.  At the time (1999), Qmail
> did not have LDAP support (correct me if I'm wrong).  Sendmail did.
> Even if Qmail did have LDAP support then, Sendmail's source was *much*
> easier to dig through for the performance tuning we did.

I'm not sure what the situation was like in 1999, now Qmail and LDAP support 
is adequate.

> Today we are very happy with our Sendmail installation.  Debian and
> Sendmail play very happily together, and with our modular setup we
> process over 4 million messages a day with over 60,000 mailboxes.  Yes,
> Sendmail has had several high-profile vulnerabilities, but with Debian
> and apt, we were able to stay on top of it with little difficulty.  I
> can see how Qmail could look attractive to a smaller site with a less
> complex setup, but for us, Sendmail was the way to go.

You need two mail storage servers for 60,000 accounts?

Recently I was running a system with over 1M accounts on 5 storage servers.  
The machines all had 4G of RAM which was necessary to keep the directory 
structure in cache.  So the servers were averaging about 2M/s of disk writes 
and only 200K/s of reads according to iostat.  Performance was OK but dropped 
out at times of high load.  I determined that using a NVRAM device (such as a 
umem card) for the primary queue would allow each server to handle twice the 
load with only a 7% price increase per server.

I am fairly confident that the same Qmail setup could handle 4M messages and 
60K mail boxes per back-end server very easily with Dell PowerEdge 2650 
machines in a fairly standard setup.

Of course there are lots of things you can do to tune performance, such as 
mounting with noatime and using a patched kernel to fix the performance 
limiting bugs (I used a SUSE kernel for the mail servers in question).

http://www.coker.com.au/selinux/   My NSA Security Enhanced Linux packages
http://www.coker.com.au/bonnie++/  Bonnie++ hard drive benchmark
http://www.coker.com.au/postal/    Postal SMTP/POP benchmark
http://www.coker.com.au/~russell/  My home page

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