Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site ucbvax.ARPA
Path: utzoo!watmath!clyde!cbosgd!ucbvax!info-vax
From: info-vax@ucbvax.ARPA
Newsgroups: fa.info-vax
Subject: Re: Dual ported TU78s
Message-ID: <5142@ucbvax.ARPA>
Date: Thu, 28-Feb-85 20:57:19 EST
Article-I.D.: ucbvax.5142
Posted: Thu Feb 28 20:57:19 1985
Date-Received: Fri, 1-Mar-85 09:50:56 EST
Sender: daemon@ucbvax.ARPA
Organization: University of California at Berkeley
Lines: 23

From: weber%delphi.DEC@decwrl.ARPA  (Ralph Weber)

RE:    With a dual ported TU78 you have three useful options on the
RE:    little POST thumb wheel on the drive:

RE:	(0)	PORT A -- the system on Port A can use the drive.  Operations
RE:				from Port B will fail
RE:	(1)	PORT B -- just the reverse of above
RE:	(2)	PORT A/B -- either system can write to the drive interleaving
RE**:				I/Os on a command by command basis.  No
RE**:				problem in a VAXcluster where the system
RE**:				software arbitrates to allocation of the tape
RE**:				drive and insists that only on process tree
RE**:				can have it at a time;
					.
					.
					.

Hold on just a cotten pickn' minute here!  VAXclusters arbitrate cluster-wide 
only for access devices which are known to be cluster accessible.  HSC 
controlled disks & tapes, MSCP served disks, and dual-ported disks qualify as
cluster-accessible.  Everything else does not.  (The system performs better 
that way.)  If I were playing this game, I'd use options 0 and 1.