dovecot replication (active-active) - server specs

[Ed W]

> we've got 2 new fileservers, they have each SSD HDDs for "new-storage"
> and 7200rpm SATA HDDs on RAID 5 with 10 TB for "alt-storage"
>

Friends don't let friends use Raid5...
     http://www.baarf.com/

(Use Raid6 or something else...)

Note, a common counter argument is that someone has "full backups and 
can survive a rebuild, so the RAID5 is really just to increase uptime".  
I suggest you do the sums on silent corruption and compare with your 
data size.  Bit rot seems to be an observable problem now. Scrub your 
arrays regularly and where possible use data integrity checks at higher 
levels (not much for linux, but ZFS offers this for other OSs)

Good luck

Ed W