mail server replication

[Colin Bruce]

Dear Paul and others,

I haven't tried it yet but it may be that DRBD  (http://www.drbd.org)
might be able to do what you want. We used it with a UW Imap server and I
don't see why it shouldn't work with Cyrus. It is probably possible to
split the users between two cyrus servers and have each group replicated
to the other server so that each server could become a server with all
users reasonably quickly. I suspect it would take a few minutes to fail
over. As I say I haven't tried this so perhaps it won't work.

Best wishes.....
Colin


On Fri, 21 May 2004, Paul Dekkers wrote:

> 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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