cyrus replication : master to replica and replica to master

[Rob Mueller]

> i'm very surprised that there is not really official point from cyrus-imap 
> dev team against using cyrus in cluster active/active mode

I can't comment, but I guess they're busy.

> Since serverals years the messaging service become very important and the 
> clustering system is the right way to provide a real fail over system
> After googlize i had read that  the only best method is to using drbd but 
> there no really wikis and documentations about implementing this kind of 
> structure.

drbd doesn't allow a master/master mode either, unless you use some 
clustered filesystem, and take the performance hit due to locked access to 
meta data (eg mailboxes.db) that would be happening.

cyrus replication does what drbd does, but has the added advantage that it's 
"content aware", so it only has to replicate the actual needed data, it can 
do checksumming of email data on both sides, and you won't lose everything 
if you get some os level file system corruption on your master.

Basically they're similar solutions (master -> slave replication) but at 
different levels (block level vs content level).

Rob