NFS vs Replication

[Gerald Galster]

>> With DNS this happens automatically because ips are rotated by resolvers
>> and the mailclient gets the same ip for all its connections. Failover
>> is builtin as mailclients just connect to the second ip when the first
>> is not reachable.
> 
> I don't trust DNS load balancing. I saw too many times a client stuck
> with the wrong (down) IP... This is my experience ;-)

Interesting, I have deployed that dns-based approach where two dovecot servers
are replicating between two distant datacenters. A few years ago one datacenter
had a major outage and new connections quickly failed over to the remaining
server. Maybe this is client specific and/or has improved over time.

If the loadbalancer/director approach works for you, that's ok.

>> Replication works reliable with mdbox/sdbox but you should avoid maildir.
> 
> I'm using and I like Maildir. There are some documentation about to
> don't use it with replication? Which are the drawbacks?

Maildir is probably the most robust mail storage format, but it is very
demanding on your disks because flags like "Seen" are encoded in the
filename. Every flag change needs IO as well as copying/moving/deleting
mails, quota, ... A maildir with 100k+ mails can impact the servers overall
performance, but as you use all flash storage that may not be a problem.

I remembered something about replication and maildir, took me some time
to find it:

https://dovecot.org/pipermail/dovecot/2017-February/107125.html

Timo said (Mon Feb 20 10:09:48 UTC 2017):

"There seems to be something weird with using Maildir and replication.
Haven't had time to debug it and it's likely not an easy bug to fix,
so for now the solution would be to use only sdbox/mdbox with replication."

I don't know if that is still the case, I can just tell mdbox works for me.


Best regards,
Gerald
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