Date: Tue, 3 Mar 1998 22:47:28 +0100 (MET) From: Wilko Bulte <wilko@yedi.iaf.nl> To: shimon@simon-shapiro.org Cc: sbabkin@dcn.att.com, tlambert@primenet.com, jdn@acp.qiv.com, blkirk@float.eli.net, hackers@FreeBSD.ORG, grog@lemis.com Subject: Re: SCSI Bus redundancy... Message-ID: <199803032147.WAA03990@yedi.iaf.nl> In-Reply-To: <XFMail.980303121451.shimon@simon-shapiro.org> from Simon Shapiro at "Mar 3, 98 12:14:51 pm"
next in thread | previous in thread | raw e-mail | index | archive | help
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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199803032147.WAA03990>