>> The problem is that S2's disk performance is a lot slower than Pi's.
>> Naturally there must be some performance penalty for having 5400RPM drives, but
>> the outcome is that Pi seems to be over 10 times faster at disk IO. They both
>> have RAID1 root with RAIDframe and follow the "only one device per bus"-rule.
> What does
> dkctl wdX getcache
> print? Try it for all disks on both machines.

The output is the same for all disks in both machines:
/dev/rwd0d: read cache enabled
/dev/rwd0d: write-back cache enabled
/dev/rwd0d: read cache enable is not changeable
/dev/rwd0d: write cache enable is changeable
/dev/rwd0d: cache parameters are not savable

-- 
Ari Sovijärvi
http://apz.fi/