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?