Date: Tue, 03 Mar 1998 16:09:52 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Wilko Bulte <wilko@yedi.iaf.nl> Cc: hackers@FreeBSD.ORG, (Julian Elischer) <julian@whistle.com> Subject: Re: SCSI Bus redundancy... Message-ID: <XFMail.980303160952.shimon@simon-shapiro.org> In-Reply-To: <199803032144.WAA03955@yedi.iaf.nl>
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On 03-Mar-98 Wilko Bulte wrote: ... > Once Upon A Time, When Power Supplies Were Still Powersupplies there were > 2 signals available: AC_OK and DC_OK. Whenever your logic (disk) saw > AC_OK negate, it was time to cleanup. After some time, dependent on how > big your powersupply capacitors were, how loaded the PS was etc you saw > DC_OK negate. Unless it is a DC/DC power supply :-) Yes, you are right, but the cost of two extra wires, two gates, a transistor, etc. is really too much. ... > Drive write caches are Evil. Every write cache without good battery > backup > is Evil. Talk to a DBMS guy about enabling disk write caches. Put > sneakers > on and be prepared to run fast... Nah, we just smile at you and put your reume in the can... Actually, there are ways around that. I promised to make them available on FreeBSD and I will. Real Soon Now. I am waiting for hardware for testing... > But then again, with VM systems that have megabytes worth of unflushed > data the best way to loose your data is to pull the plug from your server > ;-) Top said, on last make world that there are 158MB of buffers in use. This is 5 times the total disk capacity on the first Unix port I tried to compile. Scary. Terry? Any thoughts on hot-starting a Unix based PC? We need to dump memory quickly, I think. No way to preserve DRAM across BIOS resets I know of. Assuming we have the ability to dump memory quickly (see below), can we just snap a state, dump it, leave a signature and resume at power up? We had that on VAXes with VMS (Not AT&T Unix, and I do not think BSD). Memory SNAP: If you write it into a DPT controller, and the controller has enough cache to hold it, it is pretty fast. I can sustain about 2us per transaction overhead and about 120MB/Sec. This gives us about a second or two. The new DPT's can retain the cache until power returns. Even a small UPS (with poer alarms will last long enough. ---------- 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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