In this Xen setup, I think the best way to accomplish your goals is to create 6
guests:
2 x Linux Postfix
2 x Linux Dovecot
1 x Linux NFS server
1 x Linux Dovecot director
Each of these can be painfully small stripped down Linux instances. Configure
each Postfix and Dovecot server to access the same NFS export. Configure
Postfix to use native local delivery to NFS/maildir. Don't use LDA (deliver).
Ok so this is interesting. As long as I use Postfix native delivery,
along with Dovecot director, NFS should work ok?
For any meaningful use of virtualized clusters with Xen, ESX, etc, a
prerequisite is shared storage. If you don't have it, get it. The hypervisor
is what gives you fault tolerance. This requires shared storage. If you do not
intend to install shared storage, and intend to use things like drbd between
guests to get your storage redundancy, then you really need to simply throw out
your hypervisor, in this case Xen, and do direct bare metal host clustering with
drbd, gfs2, NFS, etc.
Why is this the case? Apart from the fact that Virtualisation becomes
"more useful" with shared storage (which I agree with), is there
anything wrong with doing DR between guests? We don't have shared
storage set up yet for the location this email system is going. We will
get one in time though.
