[comp.unix.ultrix] Dual-Porting under ULTRIX?

grr@cbmvax.commodore.com (George Robbins) (04/11/90)

In article <19547@boulder.Colorado.EDU> mre@ngdc2.colorado.edu (Marcus O. Ertle) writes:
> 
> Is it possible to dual-port disk drives under ULTRIX?  I've got two
> VAX/780's running Ultrix 3.1.  Each 780 has four RA81's - three of
> which are c-partitions-only.  In the event one VAX is down, I would
> like to somehow mount the c-only-disks on the other VAX.  Is it just
> a question of rebooting the VAX that's up - with a kernel that sees
> the additional 3 disks - or is there a way to access these disks
> without a reboot (with the properly configured kernel)?  Or am I
> barking up the wrong tree - and need to invest in an HSC?

Sure you can dual-port disks, as long as you understand that DEC RA type
drives only support "static dual-porting" and that Ultrix doesn't support
dual-porting at all.

What this means is that you can cable the drives to both systems and press
both the A and B buttons, however whichever system grabs the unmounted drive
first gets it.

To make this useful, you normally fsck/mount the drives from one system
via ":rw:" fstab entries.  On the other system the partitions are listed
as ":xx:" entries. If that system is down you simply do a manual fsck/mount
of the drives on the other.  If the one system has crashed and left the
drives reserved to it, you might have to pop out that systems A/B button to
make it release the drive.

You do have to have the extra drives config'ed in and have the devices
MAKEDEV'd on both systems.  I'd just make entries for say drives 0-7 on
both systems and one system would have drives 0,1,2,3 and the other
perhaps 0,5,6,7 so that when you flip the ownership of the drives, there
is no conflict.

Obviously you'll need enough UDA50's (or whatever your're using), but these
are very cheap on the used market, the SDI cables might cost you more 8-)

I ran with this sort of setup for months while converting from  785 to 5800
and never ran into any problems.

-- 
George Robbins - now working for,     uucp:   {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing:   domain: grr@cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)

mellon@fenris.pa.dec.com (Ted Lemon) (04/12/90)

Assuming that you're running Ultrix 3.1, you should be able to hook
your RA81s up to both machines, as long as you make sure that only one
machine tries to mount them at a time.   This means that you shouldn't
reference any file systems in both of the fstab files, of course.

From a mechanical standpoint, just hook up the "A" port of each RA81
to the controller on one VAX, and hook up the "B" ports to the other
VAX.

This will probably also work under previous versions of the operating
system, but I haven't tried it, and I suppose the device driver could
be hosed, so experiment at your own risk.

			       _MelloN_

schedler@src.dec.com (Richard Schedler) (04/13/90)

You should also make sure that at least one system has the dual ported 
disk designated as "xx" in /etc/fstab at all times.  If both systems have 
it designated as "rw" or "ro" and you experience a power failure, you 
could (and probably will :-) get it mounted on the wrong system at the 
wrong time.  This could lead to big problems depending on what you're 
using the disk for.

	--Richard

Richard Schedler                          Systems Research Center
schedler@src.dec.com                      Digital Equipment Corporation