You may have a "SCSI3" kernel or forced mappings from targ 0 to sd3
and vice versa.  I have seen this before, when the prom indicates the
boot device to the netbsd system and there is 0/3 confusion.
Remembering harder, I think I have only seen this when moving
filesystems around - I had both targ 0 and targ 3 each with the same
bits in sdXa, and booted from target 3, which had root on sd3a (under
netbsd native numbering).  But the fstab said 'sd0a'.  So the kernel
had sd3a mounted as /, and the remount rw failed.

Make sure you are booting off the disk that has your intended root.

        Greg Troxel <gdt@ir.bbn.com>