From owner-freebsd-hackers Tue Mar 3 15:27:56 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id PAA14756 for freebsd-hackers-outgoing; Tue, 3 Mar 1998 15:27:56 -0800 (PST) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from uni4nn.gn.iaf.nl (osmium.gn.iaf.nl [193.67.144.12]) by hub.freebsd.org (8.8.8/8.8.8) with SMTP id PAA14656 for ; Tue, 3 Mar 1998 15:27:45 -0800 (PST) (envelope-from wilko@yedi.iaf.nl) Received: by uni4nn.gn.iaf.nl with UUCP id AA20477 (5.67b/IDA-1.5 for hackers@FreeBSD.ORG); Wed, 4 Mar 1998 00:27:09 +0100 Received: (from wilko@localhost) by yedi.iaf.nl (8.8.7/8.6.12) id WAA03990; Tue, 3 Mar 1998 22:47:28 +0100 (MET) From: Wilko Bulte Message-Id: <199803032147.WAA03990@yedi.iaf.nl> Subject: Re: SCSI Bus redundancy... In-Reply-To: from Simon Shapiro at "Mar 3, 98 12:14:51 pm" To: shimon@simon-shapiro.org Date: Tue, 3 Mar 1998 22:47:28 +0100 (MET) Cc: sbabkin@dcn.att.com, tlambert@primenet.com, jdn@acp.qiv.com, blkirk@float.eli.net, hackers@FreeBSD.ORG, grog@lemis.com X-Organisation: Private FreeBSD site - Arnhem, The Netherlands X-Pgp-Info: PGP public key at 'finger wilko@freefall.freebsd.org' X-Mailer: ELM [version 2.4ME+ PL32 (25)] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG As Simon Shapiro wrote... > > On 03-Mar-98 Wilko Bulte wrote: > ... > > > This is called the 'write hole' in the literature. The trick is to > > use battery backed cache not only for RAID5 (write)performance > > reasons, but also to keep the data until date AND parity have safely > > landed on the disks. > > I have seen an interesting solution some time ago; Instead of battery, the > spindle motor (on the disk) was used to generate the power needed to flush > the caches. then the motor leads will be clamped, and the spidle shut down > quickly (normal procedure nowdays). This was done on a 14" spindle that > had a bit more inertia than todays' disks. But the circuitry consumed more > power too. > > > Same problems for mirror sets BTW. And don't enable the write caches *on > > the > > disks themselves* unless you feel suicidal ;-) > > Unless they use the above trick... > > ... The trick is cute, but it was used to park heads in the drives I saw. Not for flushing on drive caches. There would not be enough power to do e.g. a seek in order flush the cache. And by definition your platter rpm is dead wrong, you essentially use the whole thing as a electromagnetic brake. Not nice. Wilko _ ______________________________________________________________________ | / o / / _ Bulte email: wilko @ yedi.iaf.nl http://www.tcja.nl/~wilko |/|/ / / /( (_) Arnhem, The Netherlands - Do, or do not. There is no 'try' --------------- Support your local daemons: run [Free,Net,Open]BSD Unix -- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message