From owner-freebsd-fs Mon Oct 12 07:22:46 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id HAA29401 for freebsd-fs-outgoing; Mon, 12 Oct 1998 07:22:46 -0700 (PDT) (envelope-from owner-freebsd-fs@FreeBSD.ORG) Received: from magicnet.magicnet.net (magicnet.magicnet.net [204.96.116.9]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id HAA29370 for ; Mon, 12 Oct 1998 07:22:39 -0700 (PDT) (envelope-from bill@bilver.magicnet.net) Received: (from root@localhost) by magicnet.magicnet.net (8.8.6/8.8.8) with UUCP id KAA26367 for freebsd-fs@freebsd.org; Mon, 12 Oct 1998 10:20:03 -0400 (EDT) Received: (from bill@localhost) by bilver.magicnet.net (8.9.1/8.9.1) id KAA15041 for freebsd-fs@freebsd.org; Mon, 12 Oct 1998 10:12:02 -0400 (EDT) From: Bill Vermillion Message-Id: <199810121412.KAA15041@bilver.magicnet.net> Subject: Re: filesystem safety and SCSI disk write caching In-Reply-To: <199810121326.GAA09753@salsa.gv.tsc.tdk.com> from Don Lewis at "Oct 12, 98 06:26:05 am" To: freebsd-fs@FreeBSD.ORG Date: Mon, 12 Oct 1998 10:12:01 -0400 (EDT) X-Mailer: ELM [version 2.4ME+ PL38 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org Don Lewis recently said: > Even with an UPS, a large percentage of our unclean shutdowns are > power related. Most of these are due to power outages that last > longer than our UPS batteries. I don't think there is enough room > in our building to store enough UPS batteries to last through our > typical winter power outages. I don't think we'll be getting a > backup generator anytime soon, and even then I've heard quite a > few stories on freebsd-isp about problems getting generators to > reliably start. Today's UPSes typically have self-monitoring capabilities to put a signal on a pin when they reach a certain minimum capacity. At this point they will send a system shutdown command. If you have nothing as sophisticated as that, build your own. Have a normally open 110VAC relay. Connect two contacts to the TX/RX pins on an RS232. Push something through that ever minute or so. When the signal can't be passed the system will not get this signal - indicating the power has failed on the relay and it opened up (barring some other failure). If your battery is good for 20 minutes, use a routine like this. If no signal (eg no AC to relay), start timer. Set a variable to 10 Every minute check the connection. If not connected decrement the variable. If power comes up, stop countdown routine. If power still not there software monitor the relay will issue a shutdown when the counter decrements to zero. As to getting generators to reliably start - good systems from known vendors usually work well. It's the home-brew units that lack niceties. At a radio station I worked with a zillion years ago we had a motor-generator set that we were required to have (one of the EBS stations), and that had to be run once per week, also another legal requirment. It was a Ford V8 running on propane. Always started - no problems - but it was homebrew. At the end of the require hour on the air with it running all the clocks would be about 5 minutes slow and all the records play about 5-10% underspeed. Current offerings from companies such as Best - will use Onan or Sony for their small systems. Software automatically tests them once per week by starting them an running them. Options are large tanks to extend running time with no refills to days, etc. Good equipment almost never fails. Cheap equipment quite often fails - and Murphy's law dictates that it will fail when you most need it. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message