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Newsgroups: comp.unix.bsd.freebsd.misc,comp.periphs.scsi
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From: terry@spcvxb.spc.edu (Terry Kennedy, Operations Mgr.)
Subject: Re: SCSI-2 Bus Hangs
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References: <4bju5p$ihj@wilma.widomaker.com> <4bp3bp$7cc@scratchy.mosquito.com>
Followup-To: comp.unix.bsd.freebsd.misc,comp.periphs.scsi
Sender: news@spcuna.spc.edu (Network News)
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Organization: St. Peter's College, US
Date: Tue, 26 Dec 1995 17:35:18 GMT
Message-ID: <1995Dec26.123518.1@spcvxb.spc.edu>
Lines: 31
Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:11453 comp.periphs.scsi:43828
In article <4bp3bp$7cc@scratchy.mosquito.com>, boot@mosquito.com (Bruce Bauman) writes:
> We have exactly the same problem, with exactly the same symptoms. It
> only happens on our news server machine, and occurs about once a
> week or so.
A SCSI bus hang almost always indicates a hardware problem (drive firm-
ware comes under hardware here).
You need to have something on the SCSI bus to monitor activity *before*
the problem occurs. This could either be something simple like a terminator
with lots of LED's (PC Connection sells one) or an active SCSI bus ana-
lyzer. I know if you post to comp.periphs.scsi and mention bus analyzers,
several manufacturers will then send you unsolicted email/FAXes 8-).
If you use high-quality (not the same as "expensive" or "bulky") cables
and pay attention to the configuration rules, you shouldn't have SCSI bus
hangs. Of course, if there's a drive problem, all bets are off. In par-
ticular, Fujitsu drives seem to be overly picky. I use Seagate drives ex-
clusively and haven't had any problems.
Also, the driver should time out a SCSI command that's taking too long
and start recovery, first by retrying the command, then by doing a device
reset to the target, and then doing a complete SCSI bus reset as a last
resort. This is harder than it looks, though - for example, rewinding a
tape should have a much longer timeout than a disk read. The only driver
I know of that does this is the new BusLogic driver for Linux (from ftp.
dandelion.com if I recall correctly).
Terry Kennedy Operations Manager, Academic Computing
terry@spcvxa.spc.edu St. Peter's College, Jersey City, NJ USA
+1 201 915 9381 (voice) +1 201 435-3662 (FAX)