[Dovecot] Real-time sync using dsync

[Timo Sirainen]

On 27.2.2013, at 21.19, Nikolaos Milas <nmilas at noa.gr> wrote:

> Any suggestions?
> 
> I am looking for a solution that would work in creating a failover cluster with two nodes, utilizing (two) CentOS 6 VMs, each on a different data center; this requirement makes technologies like drbd unusable (due to the inherent lack of complete link reliability between the two nodes).
> 
> I was thinking that dsync might be a good foundation for such scenarios.

dsync was meant exactly for that kind of replication. For a relatively few number of users this should work well (minus the initial bugs until they get all fixed). It's a little bit heavy operation to run dsync for each small change though, so I wouldn't necessarily use it for large systems. Then again it's mainly CPU usage, and Dovecot uses normally about 0% CPU, so maybe it's not so bad.

The other possibility that is more efficient and easier to scale to large systems is to use one of the scalable object storage backends and Dovecot's object storage plugin (commercial-only, available soon).

The idea behind both of these ways is to make it easy, cheap and reliable to do multi-datacenter replication for IMAP servers. None of the cluster filesystems can do that.