Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2.fluke 9/24/84; site fluke.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxj!houxm!vax135!cornell!uw-beaver!fluke!joe From: joe@fluke.UUCP (Joe Kelsey) Newsgroups: net.unix-wizards Subject: Re: Dual porting UDA50 drives under 4.2 Message-ID: <2058@vax4.fluke.UUCP> Date: Mon, 7-Jan-85 12:25:09 EST Article-I.D.: vax4.2058 Posted: Mon Jan 7 12:25:09 1985 Date-Received: Tue, 8-Jan-85 04:16:09 EST References: <6991@brl-tgr.ARPA> Organization: John Fluke Mfg. Co., Inc., Everett, WA Lines: 30 There is a point which everyone seems to be missing here. DSA (Digital Storage Architecture) drives CANNOT be "dual-ported". They may be "dual-pathed", but it is physically impossible to "dula-port" them. What you need to consider is that a UDA50 really is not intelligent enough to be able to handle the full MSCP protocol. If you consider what happens in an HSC50 environment, then you can see the problems better. When you have a VAXcluster, centered around the HSC50, the HSC is responsible for coordinating ALL read/write access to all drives, and the VAXen communicate other information about locking files, records, etc., among themselves via the CI. In this environment, it is possible to dual-path the drives attached to a given HSC for physical redundancy, i.e., if one HSC goes down, the other one already has the cables connected to the drives and can pick up the traffic by using the dual-path connection. Thus, even in the HSC environment, only one controller can be the master of the drives once the drive goes on-line. The same thing hold true in the UDA50 case, but in this case, dual-pathing a drive gains you NOTHING, unless you have two UDA50s on your computer just in case one of them fails. In otherwords, if you want to share disks, you have several choices: 1) Wait for the Ultrix people to figure out what they are going to do about clusters, CIs, and HSCs. Then, maybe, you can buy an HSC, star coupler, a bunch of CI780s or CI750, and go to town. 2) Talk to SI about SIMACS - they claim that it runs on UNIX now. 3) Buy Massbus disks and come up with a way of mounting the disk R/W on one system with caching disabled and R/O on the other system. /Joe