Date: Mon, 18 Oct 1999 17:14:43 -0500 From: Bob Willcox <bob@luke.pmr.com> To: Stephen McKay <syssgm@detir.qld.gov.au> Cc: Wilko Bulte <wilko@yedi.iaf.nl>, freebsd-scsi@FreeBSD.ORG Subject: Re: SCSI surprise! (was: Softupdates reliability?) Message-ID: <19991018171443.B89307@luke.pmr.com> In-Reply-To: <199909020359.NAA11043@nymph.detir.qld.gov.au>; from Stephen McKay on Thu, Sep 02, 1999 at 01:59:32PM %2B1000 References: <199908311524.RAA53070@yedi.iaf.nl> <199909020359.NAA11043@nymph.detir.qld.gov.au>
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On Thu, Sep 02, 1999 at 01:59:32PM +1000, Stephen McKay wrote: > On Tuesday, 31st August 1999, Wilko Bulte wrote: > > >As Stephen McKay wrote ... > >> I'll check the drive more carefully tonight for "power terminator from BUS" > >> stuff to see if there is any possible silly stuff there. But I think the > >> fact is that sometimes it's not safe to just pull the power plug. > > > >Maybe there is something really weird about your particular drive. I can > >only repeat my experience which is different :/ > > I checked the problem drive last night. The drive was set to power its own > terminator, but the terminator is definitely off. It can also power the > SCSI bus, but that's off too. So, all looks normal. > > I'll just assume this is a rogue drive until I see another one. I still > don't understand how it's possible though. In my experiences with SCSI, I believe that just about anything is possible! I have spent several years developing SCSI device drivers and, more importantly, much of that time was devoted to testing. In many of these tests I would deliberatly use defective and/or questionable devices (its easy to collect defective SCSI devices, it turns out). Really bad stuff can occur on the bus (you really need a SCSI bus analyzer if you're doing serious SCSI testing) due to various combinations of devices, cables, and terminators. I suppose partly as a result of my experiences in my SCSI testing days (haven't done it in a few years), for production systems that I depend on, I always keep my SCSI busses as simple as possible. I try not to mix device speeds and types by installing multiple controller cards and installing all of my disks on one (or more, as necessary), and all the other devices (tape, cdrom, etc.) on a separate bus. Makes me feel better (and in my experience, increases stability). As a further anecdotal note, I once had a sudden and catastrophic SCSI bus failure on a system that had been running fine and I hadn't had open in over a year. Upon diagnosing the failure I was surprised to discover a terminator installed on one of the devices in the middle of the chain (this resulted in three terminators on the bus!). Upon removing the bogus terminator everything began working fine again. Guess some driver(s) on the bus just finally got tired of driving the additional load. :-( Bob -- Bob Willcox Don't tell me that worry doesn't do any good. bob@pmr.com I know better. The things I worry about don't Austin, TX happen. -- Watchman Examiner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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