mail server replication

Neil Schneider pacneil at
Fri May 21 04:07:39 EDT 2004

Paul Dekkers said:
> Rob,
> Rob Siemborski wrote:
>>> I hope this kind of functionality comes into cyrus once; I
>>> assume it
>>> is not there yet, I once asked this on the list before ;-) And
>>> maybe
>>> it shouldn't be too difficult, since there is already a
>>> synchronisation mechanism for NNTP in place, if I'm correct.
>> This is very hard -- if not impossible -- with only two
>> machines, at
>> the very least you'd need three in order to maintain a quorum of
>> what
>> the "real view" of the server is --
>> For example, think about what would happen if there was a
>> network
>> partition and two different messages were delivered to the split
>> servers at the same time.  It's not an easy problem to solve--
>> keeping
>> a hot spare is definately the way to go.
> I agree; but what I meant was a synchronisation mechanism that can
> synchronise a spool with/to a hot spare server - without having
> the need
> for a RAID unit with two scsi interfaces. (This way you remove
> another
> SPOF ;-))
> Maybe I see this a bit like the OpenLDAP slave/master replication
> idea:
> something must "switch" in order to make the slave the master and
> vise
> versa. Cyrus could synchronise the slave with every message
> delivered,
> or when keeping a log and synchronising the messages apart.
> Although I think Gerard likes to see both servers active at the
> same
> time, I think the (master-slave kind) synchronisation would be a
> nice
> thing to start with. On the other hand, if I see what offlineimap
> can
> do, I assume it must be possible with just 2 servers to
> synchronise
> folders in a proper way (when keeping some history and logs on
> both
> sides, of course...), am I wrong? (This looks again a bit like
> bi-directional synchronisation as with unison, instead of
> master->slave
> think as with rsync or so.)

Take a look at drbd . You can do exactly what
you are describing using drbd and heartbeat.

Neil Schneider                             
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