mail server replication

[Paul Dekkers]

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.)

Regards,
Paul

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