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- Path: sparky!uunet!cs.utexas.edu!swrinde!mips!odin!fido!zola!zuni!anchor!olson
- From: olson@anchor.esd.sgi.com (Dave Olson)
- Newsgroups: comp.sys.next.sysadmin
- Subject: Re: Turning off SCSI devices and Rel 2.1
- Message-ID: <nqab7h8@zuni.esd.sgi.com>
- Date: 27 Jul 92 05:40:31 GMT
- References: <1992Jul22.114709.9162@investor.pgh.pa.us> <4455@rosie.NeXT.COM> <1992Jul27.025718.22038@umbc3.umbc.edu>
- Sender: news@zuni.esd.sgi.com (Net News)
- Organization: Silicon Graphics, Inc. Mountain View, CA
- Lines: 40
-
- In <1992Jul27.025718.22038@umbc3.umbc.edu> brian@umbc4.umbc.edu (Brian Cuthie) writes:
- | In article <4455@rosie.NeXT.COM> amm@NeXT.COM (Alan M. Marcum) writes:
- | >Bob Peirce #305 writes
- | >> I have an HSD scanner at the end of my SCSI chain. Since I don't
- | >> use it all the time ... I like to turn it off...
- | >> Something I haven't tried is to actually disconnect the scanner
- | >> from the CD drive and plug the SCSI terminator in. That doesn't
- | >> seem like a good thing to do on a running system...
- | >
- | >The SCSI bus is actually an active bus. To function correctly,
- | >all devices on the bus should be powered on, the cables should
- | >have the proper impedence, and the bus should be terminated at
- | >both ends. A *very* short bus can be run with termination only
- | >at one end (e.g., just the on-board disk, which has a terminator
- | >on it).
- |
- | This is bunk. The SCSI bus is driven by open-collector devices. A
- | properly behaved SCSI peripheral may be left in the powered down state without
- | any ill effects.
-
- Ah, thus speaks someone who hasn't dealt with the real world. Many
- (most?) SCSI devices will pull all the bus lines into the active state
- when powered off. In fact SCSI 2 only has an implementors note (NOT a
- requirement!) suggesting that powered off SCSI devices tristate the bus
- rather than pulling the signals one way or the other. In my experience
- (and I have looked at a *LOT* of different SCSI devices), almost none
- do this yet. Yes, there are some, but not many, for a number of
- reasons (cost is one of them).
-
- | Nothing personal, Alan, but is this the kind of answer I can expect from
- | NeXT tech support at $225/Question ?
-
- Alan is right, you are wrong. Of course, if you know it all anyway,
- why would would you want to call for support ;)
-
- PS: Hi Alan; ain't supporting customers grand!
- --
- Let no one tell me that silence gives consent, | Dave Olson
- because whoever is silent dissents. | Silicon Graphics, Inc.
- Maria Isabel Barreno | olson@sgi.com
-