> > changing root device to sd1a
> > (next line I get depending on the version of the kernel, later ones give it)
> > sd1(ncrscsi 0:3:0) Does not support linked commands.
> > panic: cannot mount root
> 
> Perhaps I'm missing something, but isn't the problem stated in the
> error message? The drive doesn't support linked commands. (Are these
> the tagged commands current-users has been babbling about?) The driver
> wants the drive to do something (linked commands) which the drive doesn't.

Actually, if you get the "does not support linked commands" you're one of 
the lucky ones!  All this means is that the driver found an opportunity 
to try linked commands, and then discovered that the drive in question 
doesn't support them.  In this case the SCSI driver remembers this, and 
won't bother trying linked commands in the future!

Now, if you've got a drive that claims to support linked commands (like 
my Toshiba MK538FB) but then goes into SCSO never-never land when you try 
to give it a linked command, you're in real trouble!  :)

> Not knowing scsi innards, I can't help more. Do you get to the line
> where you identify the drive? Something like:
> 
> sd1 at scsibus0: {drive particulars}
>  targ 3 lun0: <Drive maker's name> SCSI# 0/direct fixed

The "Does not support..." occurs only after the configuration stuff is 
complete, since attempting linked commands requires that the SCSI 
interrupts be enabled.  (They're not enabled during the boot-up stuff.)