Robust Cyrus design

[Prentice Bisbal]

I've been assigned to implement a new IMAP server using Cyrus, and there 
is some disagreement as to the best design for this system. I'm seeking 
advice and opinions of those of you with Cyrus administration experience.

The problem:
I need to produce a much faster IMAP server than what is currently being 
used (UW IMAP on a ancient, overworked Origin 2000). It is expected that 
this mailserver provide some sort of failover protection.

I have at my disposal several IBM xSeries 335 servers connected to a SAN 
for this application.

Proposed Design 1:
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Create two mailservers completely identical to each other that are 
sharing the /var/lib/imap and /var/spool/imap directories through the SAN.

If both IMAP servers try to access these shared files at the same time, 
there can be problems. There are two possible solutions to this:

(a) The second system is warm spare. It only comes online in the event 
of a failure of the first one (done manually by sys admin)
(b) The (unstable) patch is applied that allows two different Cyrus 
servers to access the same files at the same time.

Proposed Design 2:
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Use 3 servers set up in a Murder aggregate as described 
http://asg.web.cmu.edu/cyrus/ag.html. It is believed that this will 
provide some failover protection, but I disagree. Again, the files will 
be stored on the SAN.

I eagerly await your input.

Thanks,
Prentice