Quoting dovecot at 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!