[Dovecot] High Availability strategies

[Joseba Torre]

Thanks a lot for all the answers. We already have high availability on 
the storage, so we'll go with Timo's proposal, mainly because it's the 
closer one to our current situation.

Thanks! 

El Sábado 25 Julio 2009 a las 01:58, Timo Sirainen escribió:
> On Jul 24, 2009, at 5:00 AM, Joseba Torre wrote:
> > we have a medium setup (8000 pop and imap users using almost
> > every available client, 800GB of stored mails using maildir on a
> > Celerra NFS server, with index files on local disks, and procmail
> > for local delivery), being served by a Dell PowerEdge 2850 (2GB
> > RAM and dual P4 Xeon 3,2GHz).
> >
> > Our current not-so-high availability setup is based on a similar
> > server with the same setup and a easy but manual process to
> > switch from one server to another.
>
> So you currenly have a single server serving all imap/pop3 users?
>
> > - The recommended setup, with each user being sent always to the
> > same server, is not possible because our load balancers (Cisco
> > Catalyst 6000) can't do that.
> >
> > - We could put both servers behind the load balancer, and keep
> > local index files on each server. Usually the same ip we'll be
> > redirected to the same server, so few problems will arise. When a
> > user is sent to a new server, index will be rebuilt so
> > performance will be bad but we should not expect other problems,
> > right?
>
> If a single server can handle all users fine, I wouldn't try
> anything special here. Just have them work as a master/slave and
> install some kind of a heartbeat to switch between them.
>
> > - We could also put the index files on a nfs share. No problems,
> > but pretty bad performance.
>
> If there's only a single server accessing the mails, you can use
> mail_nfs_*=no and the performance shouldn't be that bad.
>
> > - We could also get more ram for the servers and keep indices in
> > memory.
>
> I'd say local disk is much better.
>
> > Using deliver instead of procmail could improve performance?
>
> http://wiki.dovecot.org/LDA/Indexing
>
> > - We've also thought about some more or less weird setups, like
> > setting up a GFS filesystem for the index files, or setting up a
> > proxy on every server which redirect users to their fixed server,
> > but they seem too complex for few advantages.
>
> Assuming still a master/slave setup, you could use DRBD to
> replicate indexes between local disks.


-- 
Joseba Torre. Vicegerencia de TICs, área de Explotación