Dual-Porting under ULTRIX?

[George Robbins]

In article <19547 at boulder.Colorado.EDU> mre at 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 at cbmvax.commodore.com
Commodore, Engineering Department     phone:  215-431-9349 (only by moonlite)