Date: Wed, 14 Oct 1998 19:15:36 -0500 From: David Kelly <dkelly@hiwaay.net> To: freebsd-fs@FreeBSD.ORG, freebsd-scsi@FreeBSD.ORG Subject: Re: filesystem safety and SCSI disk write caching Message-ID: <199810150015.TAA12721@nospam.hiwaay.net> In-Reply-To: Message from Don Lewis <Don.Lewis@tsc.tdk.com> of "Tue, 13 Oct 1998 22:59:24 PDT." <199810140559.WAA17612@salsa.gv.tsc.tdk.com>
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Don Lewis writes: > On Oct 13, 11:16pm, "Justin T. Gibbs" wrote: > } Subject: Re: filesystem safety and SCSI disk write caching > } >} This doesn't follow. If the cache is disabled, it doesn't matter if > } >} the drive loses power due to hitting the reset button. We already > } >} know that losing power on a drive that cached data will not work. > } > > } >I didn't hear the sound of any mechanical things spinning down. The > } >machine just started going through its boot sequence. > } > } The drive will reinitialize to the 'power on state' if the power fluctuates > } into a zone that might invalidate it's run-time state. It doesn't take a > } very long spike for the drive's power-glitch sensor to go off. In this > } case, dropping cached contents on the floor is much safer than attempting > } to continue from an unknown state. > > If that's the reason for the problem that I saw, then the UPS the > system was plugged into wasn't sufficient to prevent the problem. Before you fight it too much more, replace the power supply. I've cured a number of "impossible" problems with a new power supply. One spectacular example was a Power Mac 7200/120. Crash, crash, crash. Sometimes it would run for 30 minutes. Sometimes overnight. Technician replaced everything several times over a couple of weeks. Everything but the plastic case and the power supply. I insisted on a new PS the last time back. And it worked like a charm. Power supply filter capacitors age with heat. And lose their ability to be good capacitors. No telling what kind of noise is on your DC power wires inside the case. Your PS could be generating a spike of its own on RESET when/if something suddenly demands a lot of current. Or if something suddenly quits demanding the current it was using. Switching power supplies need to be able to run thru a missed cycle or so. Or at least for 4 milliseconds. Inexpensive UPS's are "on-demand" and can take as long as 4 milliseconds to detect dropped power and come to the rescue. Otherwise on-demand UPS's are doing nothing. They might be acting as "surge suppressors". Bought a Best Power Inc, FerrUPS 700 a couple of years ago at a hamfest for $125. This UPS uses a ferro-resonant autotransformer and is online 100%. My voltmeter says its putting out 125VAC while my line voltage is 119. It also keeps my feet warm. -- David Kelly N4HHE, dkelly@nospam.hiwaay.net ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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