[Dovecot] Real-time sync using dsync

[Alex Crow]

On 27/02/13 20:19, Nikolaos Milas 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).

Not sure how one can provide full HA between two datacenters with a 
single unreliable link in any case. You should arrange multiple 
physically independent links before you even think about doing failover 
- otherwise you stand to find yourself in a sticky situation when 
something odd happens. DRBD "split-brain" also applies to other 
solutions such as clustered and replicating filesystems. It hurts like 
hell when your storage gets damaged and you have no way of telling what 
the "good" copy is.

*If* you can wire in a second circuit between the two DCs (and 
preferably a 3rd you will be OK for any HA scenario. Ie, one circuit for 
data+DRBD traffic (ideally this should be 2 circuits) and another for 
heartbeat/fencing etc.

That said, I've heard good things about GlusterFS but I'm still not sure 
I'd trust it for corporate-level offsite HA.

This kind of thing is cheap to do badly and expensive to do right.


Cheers

Alex