[Dovecot] Direct groups of users to pairs of backend servers

[Stan Hoeppner]

On 3/24/2014 10:02 PM, Murray Trainer wrote:
> Hi All,
> 
> I am using dovecot in the Director setup with multiple proxy and
> backend mailstores and user information stored in LDAP.  I am aware
> users can be directed to a single backend server.  It would be useful
> to be able to direct groups of users to pairs of backend servers to
> give some fault tolerance against NFS issues and make the whole thing
> more scalable.    

Your description says you currently have a "shared nothing" storage
architecture.  You can't get any more scalable than that.  To enable
"groups of users" to be directed to "pairs of backend servers" you'll
need each member of the pair to mount the NFS path of the partner server.

Then you will have two different mailbox locations to deal with.  Do you
have per user mailbox paths configured in LDAP?  You will have to do
that for this "pairing" to work.

> Otherwise each backend mailstore will need all
> the NFS mounts and the whole cluster will be affected if one NFS mount
> has an issue.  

The whole cluster will not be affected.  Only users whose mail in on the
problem mount will be affected.  This is no different that your current
setup in that regard.

> I am not sure if this possible with the current
> dovecot implementation?  If not it would be a great enhancement.

So, in a nutshell, you want Dovecot to be able to overcome faults in
your NFS architecture because you did not build in redundancy?  Is this
correct?

Why are you concerned about NFS mount failures?  Most folks running NFS
Dovecot clusters share a single mount with all mailboxes among all the
cluster nodes.  You seem to have multiple mounts, one for each backend
node.  If mount failures were a common occurrence, we'd see frequent
reports of that.  But we don't.  Did you home brew your NFS servers and
they're not reliable?

Cheers,

-- 
Stan