Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!mcdchg!ddsw1!nvk
From: nvk@ddsw1.MCS.COM (Norman Kohn)
Newsgroups: comp.unix.i386
Subject: Re: Re: < 3 SCSI Drives on ISC 2.02 (problem) >
Summary: motor start command?
Message-ID: <1990Aug09.001023.2332@ddsw1.MCS.COM>
Date: 9 Aug 90 00:10:23 GMT
References: <675@unlisys.UUCP> <3491@tmiuv0.uucp> <11090@alice.UUCP> <1990Aug03.132554.13326@scuzzy.mbx.sub.org>
Reply-To: nvk@ddsw1.MCS.COM (Norman Kohn)
Distribution: comp
Organization: ddsw1.MCS.COM Contributor, Wheeling, IL
Lines: 31

In article <1990Aug03.132554.13326@scuzzy.mbx.sub.org> src@scuzzy.mbx.sub.org (Heiko Blume) writes:
>debra@alice.UUCP (Paul De Bra) writes:
>>?possible that your supplies are crowbarring.
>
>>There is a potential problem indeed, but what's most important is how
>>power hungry the drives are. I don't know about the Quantum but the
>>Wren V only needs about 15 Watts (average), while a Seagate 4096 or similar
>>drive needs almost twice as much.>
>the danger is how much the drives need when you power them up. i RTFM'ed
>a bit and found out that my 600MB WREN V uses up to 4.5 ampere on startup
>(on 12V). well, most 220 watt power supplies can give you 8 ampere on 12V
Some drives (my CDC-Imprimis, for example) have a jumper option
of not starting the motor until receiving a "motor start" SCSI
command.  The drives could thus be started one at a time.
This could even be done within the unix startup processes:
the drive with the root filesystem could be left to start
at power on, and the rest powered up via commands in
/etc/rc2.d.  I haven't tried this, though, and wouldn't know
how to issue the commands to the SCSI interface.  ISC
clearly doesn't want us talking to the interface, and I
imagine that you'd have to dig quite a bit in the driver code.
It would probably be easier to write a separate driver
that does nothing but send the startup signal to the SCSI port:
if it functions only during system startup, perhaps
it can exist in ignorance of the state of the "real" SCSI driver.


-- 
Norman Kohn   		| ...ddsw1!nvk
Chicago, Il.		| days/ans svc: (312) 650-6840
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