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!ihnp4!ucbvax!info-vax From: info-vax@ucbvax.ARPA Newsgroups: fa.info-vax Subject: Dual ported TU78s Message-ID: <5129@ucbvax.ARPA> Date: Thu, 28-Feb-85 04:40:52 EST Article-I.D.: ucbvax.5129 Posted: Thu Feb 28 04:40:52 1985 Date-Received: Fri, 1-Mar-85 20:07:24 EST Sender: daemon@ucbvax.ARPA Organization: University of California at Berkeley Lines: 28 From: Bill Mitchell We're beginning to lose our fascination with buying TU78s at $30k a whack and are contemplating dual porting a TU78 between two 785s. I haven't been able to get an entirely confident answer from DEC about how software interacts with the dual-ported device, so I thought I'd ask the list. The machines in question will be running UNIX (4.2bsd). The basic question is: When one machine is using the tape, how does the tape drive appear to the other machine? Does it appear to be off-line? Would concurrent operations by both machines just overlap? One person from DEC that I was talking to gave me the impression that if you started both machines writing a tape, the writes would just interleave in some arbitrary fashion. That is, if a write was in progress by one machine, a transaction by the other machine would just wait; i.e., the locking is on a per-operation basis. I would consider this to be entirely satisfactory as long as (obviously inadvertent) concurrent usage didn't sufficiently confuse one or both of the drivers enough to crash the system. Does anyone have experience with dual-ported TU78s on 4.2? What are the facts? Thanks in advance, Bill Mitchell whm.arizona@csnet-relay {ihnp4,noao,mcnc,utah-cs}!arizona!whm