High availability mail server options

[Les Mikesell]

On Tue, 2005-10-04 at 15:30, David Hollis wrote:
> > 
> > > 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.
> > 
> > If you are going to the trouble of providing redundancy, I'd think
> > you'd want to back up all of the user's data, not just email, so
> > having it all in the same place becomes an advantage for maildirs.
> > Also, the cyrus database format may have some internal dependencies
> > that will break if you copy it without shutting down.  The maildir
> > format was designed so the messages were self-contained and do
> > not need multiple operations to be atomic.  Dovecot tries to keep
> > an index which will most likely be wrong if copied when the user
> > is active, but it will rebuild it if it becomes inconsistent.
> > 
> 
> Yeah, the dovecot index stuff I'm hoping really isn't an issue.
> Hopefully it picks up that things it's out-of-whack and updates itself.
> As for user data, there isn't any on this system, it's just mail so I
> only need to replicate the mail partition contents and the LDAP
> directory part.  LDAP will use OpenLDAPs replication of course so that
> part isn't an issue.

If you really need down-to-the second replication you might look at
the raid-over-network options - drbd or raid over enbd devices.  But
a 'warm' backup server kept up to date with frequent rsyncs is
going to be a lot better than most other ways you would handle
backup/restore and server crashes.

-- 
  Les Mikesell
    lesmikesell at gmail.com