On 2/27/13 3:10 PM, Timo Sirainen wrote:
On 27.2.2013, at 21.19, Nikolaos Milas <[email protected]> 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.
Timo, has this been tested on large systems yet? I plan on hammering a
two node dsync cluster running 2.2rc2 (each node is 100 miles apart in a
different data center connected via 10gb ring) with a SMTP/IMAP/POP
generating bot cluster we have in our test network to see how well it
scales. I will update with my findings next week when I get a chance to
work on it. I have to +1 Nikolaos' sentiment for a geographically
distributed mail cluster, we have been hoping for a Dovecot solution to
this problem for the last few years.
