> > RAID tuning could be a whole other document :)
>
> Sure, where is it? :-)
>
> What does it mean when CPU is 99% idle, RAID is 100% busy, and the RAID
> components are 0.2% busy?  This happens while formatting a RAID partition,
> but similar numbers happen during other operations as well.
>
> Why is RAID completely busy while the disks are almost idle?
>
what you use for measuring?

sysstat?

sysstat shows always at least 99% disk load on one of my system, even when
nothing is going on