[Dovecot] High Availability strategies

[Joseba Torre]

Hi,

we have a medium setup (8000 pop and imap users using almost every 
available client, 800GB of stored mails using maildir on a Celerra NFS 
server, with index files on local disks, and procmail for local 
delivery), being served by a Dell PowerEdge 2850 (2GB RAM and dual P4 
Xeon 3,2GHz).

Our current not-so-high availability setup is based on a similar 
server with the same setup and a easy but manual process to switch 
from one server to another.

We are thinking about  setting up some kind of serious high 
availability, but for every strategy we think about some problems 
appear, and I'd like to hear your opinions about them:

- The recommended setup, with each user being sent always to the same 
server, is not possible because our load balancers (Cisco Catalyst 
6000) can't do that.

- We could put both servers behind the load balancer, and keep local 
index files on each server. Usually the same ip we'll be redirected to 
the same server, so few problems will arise. When a user is sent to a 
new server, index will be rebuilt so performance will be bad but we 
should not expect other problems, right?

- We could also put the index files on a nfs share. No problems, but 
pretty bad performance.

- We could also get more ram for the servers and keep indices in 
memory.

How can we compare these solutions? Apart from performance, are other 
problems expected? Using deliver instead of procmail could improve 
performance?

- We've also thought about some more or less weird setups, like 
setting up a GFS filesystem for the index files, or setting up a proxy 
on every server which redirect users to their fixed server, but they 
seem too complex for few advantages.

Any recommendations? How are you doing this? 
-- 
Joseba Torre. Vicegerencia de TICs, área de Explotación