Multi-server but small scale

[Martin Johannes Dauser]

Hi,

if you have only one pair of servers, I think replication via dovecot's
dsync (or doveadm via ssh) where each server holds all emails as a
local storage would be easiest. 

There is a caveat with shared folders though. And dovecot replicates
only emails. The index is not included, which means for example that
you'd need 2 databases for quota - otherwise emails would count twice.
Well and any manual index management needs to be done on both sides.

https://wiki.dovecot.org/Replication

Running a cluster filesystem or NFS as a common base is possible but
needs some adjustments of dovecot like turning off caching or memory
mapping, which in turn decrease performance.

This is only some short handbook knowledge as I haven't implemented
replication yet.

Greetings
Martin Johannes Dauser

On Mon, 2018-11-19 at 17:51 -0800, Daniel Miller wrote:
> I have a small but critical server that supports our group.  As a
> single 
> server - it's obviously a single-point-of-failure for lots of
> things.  
> As I just experienced...again.  It was a lot more fun building
> systems 
> from components when I was younger...
> 
> Previously 3rd-party hosted solutions didn't look attractive for
> several 
> reasons...but I'm seeing prices now for cloud virtual machines that
> are 
> stupid cheap.  Even if they wind up being limited speed &
> availability - 
> it would seem they'd be a lot better than nothing!
> 
> So I'm considering having at least one backup server for various 
> services - obviously that includes mail.  So now I have to wonder
> about 
> the backend.  And while I think I'm reasonably current with
> networked 
> file systems (not distributed or cluster) I haven't played with 
> replication for a quite a while.
> 
> For this particular usage (I'm envisioning two servers total) - is
> there 
> a need/reason to use any form of networked/distributed/cluster file 
> storage?  Or would this be accomplished via "pure" Dovecot - dsync 
> replication would keep things updated between the servers and
> director 
> would handle the connections?  So with identically configured SMTP 
> servers, passing to the local LMTP agents, the file system would be 
> "purely local" with no NFS or other interconnection?
>