Quoting dove...@corwyn.net:
As I look at upgrading the mail server, I'd like to change to a higher availability configuration (where the server can fail and I don't have to reconfig my imap users).
Sounds like a great plan!
For the SMTP that's easy, because I can use multiple MX records, and I can redirect a port forward from one server to another. But IMAP doesn't have the same functionality, because it's the storage that matters.
True for SMTP as long as you handle the SSL certificate issue, or don't use encryption. For IMAP to be truely HA, you will need shared storage of some sort.
What's the "best" way to do that? Clustered servers using a SAN? NAS? some sort of appliance in front? Suggestions?
There is no single "best way" since it will depend on your budget, skills, etc. Certainly a SAN is one way to go, and allows for possibly active-active setups (depending on file system) and great flexibility. You could also try that with NAS if you are careful enough. SAN is more complex to setup than a NAS, but NAS is harder to setup correctly for dovecot than a SAN would be, so flip a coin there. You can "emulate" a SAN with something like DRBD if budget doesn't allow a real SAN (that is what I do). Or you could do multi-attached active-passive disk systems (external disk tray is physically connected to 2 machines in active-passive setup). Which to use depends on knowledge/skill, costs/budget, type of cluster/failover needed, vendor support if that matters to you, etc. I setup mine as a pair of redundant front-end firewalls (linux heartbeat) which connect to a trio of Red Hat Cluster Suite machines using DRBD+GFS (two nodes do DRBD+GFS and handle SMTP+POP3+IMAP4, while the third node does _NOT_ do DRBD+GFS, and simply does the webmail interface).
Thanks! Rick
-- Eric Rostetter The Department of Physics The University of Texas at Austin Go Longhorns!
