I'm trying to benchmark raidframe (level 1) with different options.

First: Where can I find a good document about raidframe?  man raidctl
is good for raidctl, but it doesn't tell too much about raid tuning.
For example, what is the maximum value of sectPerSU?  I have tried 64
and 128 and 128 gave me better performance, so I wanted to try 256,
but when I raidctl -C, raidctl -I, and raidctl -iv, I get

WARNING: raid0: total sector size in disklabel (16776704) != the size of
raid (16776960)
Initiating re-wrrite of parity
aid0: IO Error.  Marking /dev/wd1f as failed.
raid0: node (Rod) returned fail, rolling backward
WAKEUP CALLED
raid0: IO Error.  Marking /dev/wd0f as failed.
raid0: node (Rod) returned fail, rolling backward
Unable to verify raid1 parity: can't read stripe
Could not verify parity
raid0: Error re-writing parity!
Parity Re-write status:

After this, raidctl -u panics the system, I have to boot in single user
mode etc.  Is 256 an illegal value for sectPerSU?  If so, why doesn't
the manual say so?

(What is a clean way of wiping away the old raid parameters, anyway?
When I raidctl -C with new parameters, it still claims the raid disk is
clean!)

My disks are reasonably fast (49 MB/s per disk when reading two disks
simultaneously using dd), but raidframe is slower than with my previous
machine that had slower disks (and the same motherboard).

  -jm