High availability mail server options

[Craig White]

On Tue, 2005-10-04 at 11:27 -0400, David Hollis wrote:
> On Tue, 2005-10-04 at 06:13 -0700, Craig White wrote:
> > On Tue, 2005-10-04 at 08:03 -0400, 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.  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)
> > > 
> > > 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).
> > > 
> > ----
> > I think you will find that most IMAP servers aren't real keen on using
> > an NFS storage backend anyway. I can't conceive how maildir data store
> > has anything to do with replication. GFS would work - cyrus-imapd also
> > offers murder for a multi-server approach. Backup is always a bear on
> > these things that you have to consider.
> > 
> 
> Where I see Maildir helping is that the messages are stored in
> individual files instead of very large mbox files.  Once a message is
> replicated, most of the time it won't need to be replicated again unless
> something changes on it (marked as read, urgent or whatever).   It would
> seem that replicating 1GB worth of small files with a large number of
> the files being static would be easier than a 1GB single file that is
> constantly changed.  
----
OK - point made - sort of an rsync which makes sense.

I guess the things that come immediately to mind when I see you ask
this...

1. I am not sure that I would use Fedora anything for HA intent. I would
probably use RHEL or CentOS or Debian or something in the stable
category

2. A Maildir setup would likely put each users folders in their home
directories making it extremely difficult to backup the mail itself
whereas something like cyrus-imapd has it's own mail store which can be
put onto it's own partition and could simply be dumped.

3. Whichever mail delivery agent you settle on is gonna have it's own
methods of failover (if any) and backup (if any) and some consideration
needs to be given to the choice. Whether you can use NFS or GFS or some
other SAN would be indicated by the mail delivery agent - not
necessarily the type (Maildir or mbox or ???) - though I wouldn't choose
mbox as a store type any more.

Craig


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