From: Stan Hoeppner (stanhardwarefreak.com)
Date: Fri Oct 29 2010 - 00:57:59 CDT

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Victor Duchovni put forth on 10/28/2010 2:00 PM:
> On Thu, Oct 28, 2010 at 11:41:17AM -0700, Peter wrote:
>
>> I want to use postfix for active/active mode.
>
> No, you want to cluster your mailstore (IMAP, POP, ...). This is not
> Postfix. Multiple Postfix MX hosts do not need to be clustered, the
> SMTP design automatically load-balances multiple MX hosts.
>
> In an HA environment, your front-end SMTP servers would not be where
> you store your mail, rather the clustered IMAP servers would be behind
> the MX hosts, which are not clustered.
>
> Designing a clustered mail store is an interesting problem, but really
> a Postfix issue.

I think Victor meant "not" a Postfix issue. If you want to build a mail
store cluster over a WAN link, start your reading here:

http://www.drbd.org
http://sourceware.org/cluster/gfs/

The combination of these will allow you to accomplish your cluster goal.
 Depending on the aggregate write bandwidth of your MTAs and delete b/w
of your POPD, you may need a site-to-site link of anywhere from 10Mb/s
to 100Mb/s, or maybe even more. If your two servers are located in
buildings on the same campus and connected via 100/1000Mb/s ethernet
then this solution will work very well. If your two servers are located
in two internet colocation facilities and your b/w is limited to 10Mb/s
or less, RTTs are unstable, etc, then this solution may not work well
for you. Mirroring a disk over a network requires a stable quality network.

If your network is stable and the bandwidth sufficient, this is the way
you want to cluster across a network. If you lack the network
prerequisites, you're not going to be able to effectively implement an
active/active cluster with the solution above or any other.

--
Stan

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