High availability mail server options

[Les Mikesell]

On Tue, 2005-10-04 at 07:03, David Hollis wrote:
> For my company, I've setup a mail/groupware environment that uses
> Postfix, OpenLDAP, Postgres, Apache, etc and am now looking at ways to
> make it a more redundant arrangement.  All of the components have
> methods to help me with the lone exception of the backend mail storage
> for the end users.  Ultimately, I am wanting to have systems at
> different geographic locations, not even on the same network, ideally
> with users able to access any of them at anytime and be able to do their
> thing.  The users mail storage is in Maildir format which seems like it
> will help any replication type scenario.   I can't just NFS mount the
> mail directories, because then my NFS server becomes my single point of
> failure. 

One of the points of using the maildir format when it was invented was
that it worked on NFS, and back then the way to make NFS reliable was
to run it on an appliance like the NetApp filer, and if a single unit
wasn't reliable enough you could get them with remote mirroring.  These
days you might be able to find something cheaper, but the same concept
should work.

> Do things like GFS work to handle this?  If so, do they
> operate across slow links (not talking dial-up here, but general
> Internet cable/DSL type links)

Is GFS production-ready?

> If it helps, our total mail volume is not that tremendous so completely
> instantaneous replication isn't totally necessary, but I would want
> fairly quick convergence (say 30 minutes or less).

You could cycle through the maildir directories with rsync to a
failover location pretty quickly - or even take everything in
home directories if it doesn't change too much.  However you
need something different if you expect to access the different
copies at the same time and propagate changes both ways.

-- 
  Les Mikesell
   lesmikesell at gmail.com