> >
> > on a you do newfs, installboot and cp kernels on both disks (first would
> > be used for booting, second as a copy).
> >
> > bootloader loads kernel from partition a, all rest goes from RAID.
>
> Where do you put the "root" disk? On a RAID device hard coded in the kernel
> configuration?
>
yes exactly

root at raid0a dumps on none (or raid0b what you prefer).