Re: HA Mail Server

On Fri, Sep 20, 2002 at 09:54:42AM -0400, Jeff Bearer wrote:

> I'm researching setting up a 2 node cluster for providing SMTP/POP3/IMAP
> services.  I'm currently running a HTTPD cluster so I understand all the
> details of setting up the fail over etc.
> 
> The question I'm wondering about is what methods are the best for doing
> this and the best way to manage the mail spool files. and whether I'd
> want to use Fail Over or if I can use a Load Balanced configuration.
> 
> This shouldn't be too different than a HA file share, etc. but since
> I've only dealt with rsyncing infrequently changing files to web
> servers, this looks like it might be more complicated to maintain data
> integrity. 
> 
> Any tips are appreciated, Thanks

The following is just my opinion of what would make the most solid setup
for a HA mail server cluster.

1. Get ahold of three boxes. I'll name them mail1, mail2 and spool.
2. Spool should have plenty of disk for Mail spool files, as well as the
Operating system with NFS server capability.
3. Mail1 and mail2 just need the OS, NFS client capability and mail software.
My recomendation here goes to postfix or qmail. Also, make sure that your
POP and IMAP software have MailDir support.
4. Have spool NFS export the mail spool directory.
5. Have mail1 and mail2 NFS mount the mail spool share.
6. Configure the software in mail1 and mail2 to use the mail spool share to
store e-mail messages.

Alternatively, you could use a shared disk device (shared SCSI, Fiber Channel)
and a shared filesystem like GFS (http://www.sistina.com/products_gfs.htm)
instead of the spool server.

This solution has the added benefit of being highly scalable, since you can
keep adding nodes (mail3, etc) as server load increases. Once your mail spool
access speed becomes the bottleneck, you can improve performance by several
means:

1. Use a separate network segment to access the mail spool.
2. Increase network bandwith using ethernet bonding (etherchannel) or Gigabit
ethernet.
3. Add more spool space on a separate disk device and/or processor.

I see that there is still a SPOF in these, and that is the mail spool machine,
but I still haven't figured out a way to overcome that, so any suggestions are
welcome.

Cheers,
-- 
Javier Gostling
Ingeniero de Sistemas
Virtualia S.A.
[email protected]
Fono: +56 (2) 202-6264 x 130
Fax: +56 (2) 342-8763

Av. Kennedy 5757, of 1502
Las Condes
Santiago
Chile

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