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- Path: sparky!uunet!rosie!NeXT.COM
- From: amm@NeXT.COM (Alan M. Marcum)
- Newsgroups: comp.sys.next.sysadmin
- Subject: Re: Turning off SCSI devices and Rel 2.1
- Message-ID: <4455@rosie.NeXT.COM>
- Date: 23 Jul 92 18:05:11 GMT
- References: <1992Jul22.114709.9162@investor.pgh.pa.us>
- Sender: news@NeXT.COM
- Reply-To: amm@NeXT.COM (Alan M. Marcum)
- Lines: 36
-
- 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).
-
- If a device doesn't receive power, it might not pass the bus
- signals through correctly. If it's at the end of the chain, the
- terminator probably requires power to operate correctly.
-
- For the same reason you shouldn't remove a device from the SCSI
- bus while the system is running, your shouldn't power off a
- SCSI device while the system is running. Yes, these things
- MIGHT work. But, do you want to risk your data? We've seen
- instances where an improperly terminated SCSI bus can lead
- to data corruption on the internal hard disk....
-
- What to do? Talk with the scanner vendors and ask them to
- provide a "standby" mode, where the SCSI bus receives the
- proper power, but the scanning light is shut off. (Caveat:
- there might be scanners which do this already, and there
- might be SCSI devices which handle bus signals and termination
- when powered off. Check with the device manufacturer to
- be certain.)
- --
- Alan M. Marcum
- NeXT Tech Support
- amm@NeXT.COM
-