>> I'm working on installing the IBM 1G drive from my Mac into my DECstation
>> 3100 running NetBSD/pmax. I have the drive installed, there are no
>> partitions on it currently, and I have the following entry in my fstab:
>> 
>> IBM: \
>>         :dt=SCSI:ty=winchester:ns#108:nt#4:nc#4903:\
>>         :pa#1048576:os#0:ba#8192:fa#1024:\
>>         :ta=4.2BSD:
>>                         
>> I tried to do a 
>> 	disklabel -w -r rz2 IBM
>> to write the disklabel. It tells me: 
>> 	disklabel: ioctl DIOCSDINFO: Open partition would move or shrink

Try partition C instead of having A that cover entire disk space.

It's somehow outdated way to edit /etc/disktab.  You could build disklabel
in less ackwardly with text editor;

	# disklabel -r rz2  >/tmp/IBM

You would obtain human editable disklabel in the file which contains
valid SCSI parameters.  Then, adjust C partion size as;

  ...<snipped>...
  1 partitions:
  #
   c:  1048576    0     4.2BSD   1024    8192

New disklabel can be applied with disk drive;

	# disklabel -r -R rz2 /tmp/IBM

Verify whether following output matchs with your /tmp/IBM file as; 

	# disklabel -r rz2

Tohru Nishimura
Information Technology Centre
Nara Institute of Science and Technology