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Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!msuinfo!agate!howland.reston.ans.net!europa.eng.gtefsd.com!MathWorks.Com!noc.near.net!hopscotch.ksr.com!jfw From: jfw@ksr.com (John F. Woods) Newsgroups: comp.os.386bsd.questions Subject: Re: Disapearing Disks? Date: 9 Sep 1994 15:59:16 GMT Organization: Kendall Square Research Lines: 32 Message-ID: <34q0ok$5sq@hopscotch.ksr.com> References: <341uf9$d4@shore.shore.net> <CvHGot.B7x@tfs.com> NNTP-Posting-Host: kaos.ksr.com julian@tfs.com (Julian Elischer) writes: >In article <341uf9$d4@shore.shore.net>, Robert Withrow <witr@rwwa.com> wrote: >>FreeBSD 1.1.5.1, AHA1542, three Maxtor LXT312S drives, one Sony CDU541, >>one Viper 2150S tape. >>Recently I have been experencing a situation where, after the system >>has been running for a while one or more if the disks will cease to >>be available and I get a ``Unit Attention'' on them, and they become >>de-configured. >I would suspect your power supply. >The "Unit Attention" is produced by the DRIVE and not by the driver >(though it relays it to you). This usually means that a removable pack >has been changed, or that the drive has been off-line for some reason >and has come back on.. In my experience this is usually because >something caused them to start their 'power-fail' sequence. I would second this suggestion, and suggest further that you carefully total up how much current the disk drives take when seeking and how much +12V your PC supplies. A lot of PC power supplies have inadequate +12V current for lots of disk drives, especially for current spikes caused when several drives seek at once (or nearly so). With some drives, even a brief excursion of +12 beyond the +- 5% limit (or 10%, depending on the drive) will trip the power- fail protection. (I saw a system many years ago with 4 200MB Hitachi drives (when 200MB 3.5" disks were something to marvel at :-) where all four drives would mysteriously spin down when the system got busy. It turned out that the drives' +12V current requirements were listed as something like .5A running, 2A "typical", and 4A peak -- and the poor power supply couldn't handle being asked to 12-16A of +12V all at once...) Note that a lot of PC power supplies generate +12V as a sort of side-effect of running the +5V supply; hence the power supply might give a maximum current rating for +12V that only holds if the +5V supply is *also* loaded to the maximum rating.