How do I boot off of a 2nd controller?

[Chris Torek]

In article <3661 at bloom-beacon.MIT.EDU> nessus at athena.mit.edu (Doug Alan) writes:
>... boot a VAXstation-II from a disk drive on a second disk controller.

Ultrix may support several uda50 controllers on one bus.  4.2 and
4.3 BSD do not.  In 4.xBSD, one does

>... I get the Unix boot prompt:
>
>	Boot
>	: ra(4,0)vmunix

or more generally,

	xx(y,z)pathname

where `xx' is one of `hp' `ra' `up' and a few others.  `z' is just
the partition (on disks at least).  `y' is computed as

	8 * bus_adapter_index + slave		(note 1)

Hence ra(4,0) is adapter 0 (uba0) unit 4 (slave 4).  Note that
there is no room for a controller index!

-----
[1] `bus adapter index' is actually `SBI TR - 3' for UBAs on
SBI Vaxen, and `UBA nexus - 3' on 750s and 730s.  Hence the
built-in uda50-unibus in an 8600 is ra(16,z) through ra(23,z),
since this UBA is at TR 5.  For MBAs, it is `TR - 8' (or nexus
minus 8 on 750s).  The second SBI on an 8600 is indicated by
an MBA index >= 4 (this may not be in 4.3BSD).
-----

Under 4.3-tahoe the format will be

	xx(a,b,c,d)pathname

where `a' is the adapter index, b is the controller, c is the 
drive, and d is the partition.  (Multiple SBIs on 8600s will
still be kludged with mod-4 or perhaps mod-8 values for `a'.)
8200 BI adapter indicies will not be node numbers (unless we
change this), but rather determined by the actual index, such
that the first BUA (counting up from node 0) is uba0 and the
second is uba1.  (Example: two BUAs, one at node 6 and one at
node E; the one at node 6 is uba0 and the one at E is uba1.)

>Also, how does the boot program know where different
>partitions begin?  I can configure the kernal so partitions begin
>wherever I want them to.  How does the boot program know where I've
>configured the various partitions to begin?

It does not.  The partition offsets are compiled into the various
standalone drivers.  In 4.3-tahoe the partition offset in the label
overrides, assuming there is a label.  Most of the standalone
drivers support labels, although as yet only the hp and uda/ra
Unix drivers use them.  (The 8200 KDB50 driver does not; it needs
to be re-merged with the UDA50 driver.  Sigh.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris