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

[Ed W]

Re XFS.  Have you been watching BTRFS recently?

I will concede that despite the authors considering it production ready 
I won't be using it for my servers just yet.  However, it's benchmarking 
on single disk benchmarks fairly similarly to XFS and in certain cases 
(multi-threaded performance) can be somewhat better.  I haven't yet seen 
any benchmarks on larger disk arrays yet, eg 6+ disks, so no idea how it 
scales up.  Basically what I have seen seems "competitive"

I don't have such hardware spare to benchmark, but I would be interested 
to hear from someone who benchmarks your RAID1+linear+XFS suggestion, 
especially if they have compared a cutting edge btrfs kernel on the same 
array?

One of the snags of md RAID1 vs RAID6 is the lack of checksumming in the 
event of bad blocks.  (I'm not sure what actually happens when md 
scrubbing finds a bad sector with raid1..?).  For low performance 
requirements I have become paranoid and been using RAID6 vs RAID10, 
filesystems with sector checksums seem attractive...

Regards

Ed W