Recommendations for redundant server esp. regarding shared storage?

[Christian Hammers <ch@lathspell.de>]

Hello

I'm looking for some good ideas how to design a redundant mail server (maily the POP3/IMAP and data storage and not the pure SMTP relay part).

We already tried a combination of two server with mon, DRBD and NFS which was simply to complex and error prone i.e. we often had the case
that one server did not shut down due to NFS mounts which were not visible or DRBD syncing way too slow. So this time it should be something simple that everybody can handle in a case of emergency like
powerloss at night etc.

As far as I can see the main question is
 - shared storage i.e. two computers and one external SCSI RAID
   or one external NFS RAID
 - separate storage i.e. each computer has it's own internal RAID
   and one standby is rsyncing the master server and waiting for
   maybe manual command to take over the IPs.

Shared storage would be neat as we could do real load balancing on
POP3/IMAP servers as well but has anybody a recommendation for a
NFS (or something else?!) backend that is really reliable so that
suddenly dead hosts causes no problem?
(and of course which has a stable NFS, my last Arena RAID in '98
causes NFS errors itself on certain commands so we had to give it
back :-()

thanks in advance,

-christian-