Depends.

If you want to label a disk with boot blocks that are compatible with the 
system the is currently running on the machine, then typing
         disklabel -B sd0
would do the trick.

If you're trying to use the Alpha2 snapshot of 1.5 then nothing will help 
you except to get a new kernel because, as reported here earlier, the SCSI 
support on the M3100 is broken.

If you're trying to "upgrade" your boot blocks (that is to say you're 
running 1.4 and you need to upgrade to the 1.5 boot blocks but you're still 
using 1.4 during the install) then you need something like
         disklabel -B sd0 -b /mnt/usr/mdec/sdboot

--Chuck

At 02:42 PM 10/2/00 -0500, John Hayward wrote:
>Dear Vax People,
>    How does one write a bootstrap for an scsi disk on 3100?  I see in
>/usr/mdec sdboot but no bootsd.  Both man pages for disklabel and
>installboot seem to imply there may be both boot blocks and a bootstrap
>program.  I do see a boot program but not one labeled sdboot.
>    Should I have a sdboot program?  Should I explicitly refer to the
>boot program for the secondary boot?  Should I be able to boot with just
>the boot blocks?
>    TIA for pointers suggestions.
>johnh...