Date: Tue, 03 Mar 1998 16:57:21 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Karl Denninger <karl@mcs.net> Cc: hackers@FreeBSD.ORG, Julian Elischer <julian@whistle.com>, Wilko Bulte <wilko@yedi.iaf.nl> Subject: Re: SCSI Bus redundancy... Message-ID: <XFMail.980303165721.shimon@simon-shapiro.org> In-Reply-To: <19980303180959.19173@mcs.net>
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On 04-Mar-98 Karl Denninger wrote: ... > Well, if you have a big enough cap on the output side of the regulator > you > can write the rest of the current sector. But these days, trying to get > that on the circuit board is basically impossible. There is a problem with that too. Increased capacitance does funny things to switching power supplies. I think the whole idea went the way of good sound when Hi-Fi turned into solidstate stereo. ... > This is one of the reasons I like the CMD RAID controllers. They have a > nice big cache on them (with appropriate SIMMs), but they ALSO have an > input for a 6V gelcel battery, and an internal *charging circuit* to > manage it. Question is; Do they actually know how to do something useful with that cache? Or is the reset that comes from the BIOS wipe them clean? Before you answer, try it. I have seen batteries on computers before. They do not always do what you think they should. > In addition, they have inputs on them to sense UPS health (if you have > one). > > You therefore get three levels of protection: > > 1) If the UPS goes onto battery, the unit starts "watching" things. > > 2) If it gets a low power warnings (ie: the "2 minute warning") > it flushes the cache and goes into write-through mode. Now > you're "safe" if you get screwed. > > 3) If you get dumped without warning, the battery is there and it will > pick up the pieces when power returns. > > Note that if you have no battery connected or its discharged (the > controller > is smart enough to know), getting a 2-minute warning flushes the cache > and > quiesces the controller IMMEDIATELY. > > These controllers will not operate without either a battery or UPS, and > both are (of course) preferred. That's the way I like it. Except, if the O/S is not in the loop, it may do stupid things. ---------- Sincerely Yours, Simon Shapiro Shimon@Simon-Shapiro.ORG Voice: 503.799.2313 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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