[Dovecot] Better to use a single large storage server or multiple smaller for mdbox?

[Emmanuel Noobadmin]

I'm trying to improve the setup of our Dovecot/Exim mail servers to
handle the increasingly huge accounts (everybody thinks it's like
infinitely growing storage like gmail and stores everything forever in
their email accounts) by changing from Maildir to mdbox, and to take
advantage of offloading older emails to alternative networked storage
nodes.

The question now is whether having a single large server or will a
number of 1U servers with the same total capacity be better? Will be
using RAID 1 pairs, likely XFS based on reading Hoeppner's
recommendation on this and the mdadm list.


Currently, I'm leaning towards multiple small servers because I think
it should be better in terms of performance. At the very least even if
one node gets jammed up, the rest should still be able serve up the
emails for other accounts that is unless Dovecot will get locked up by
that jammed transaction. Also, I could possibly arrange them in a sort
of network raid 1 to gain redundancy over single machine failure.

Would I be correct in these or do actual experiences say otherwise?