Date: Tue, 03 Mar 1998 12:14:51 -0800 (PST) From: Simon Shapiro <shimon@simon-shapiro.org> To: Wilko Bulte <wilko@yedi.iaf.nl> Cc: sbabkin@dcn.att.com, tlambert@primenet.com, jdn@acp.qiv.com, blkirk@float.eli.net, hackers@FreeBSD.ORG, (Greg Lehey) <grog@lemis.com> Subject: Re: SCSI Bus redundancy... Message-ID: <XFMail.980303121451.shimon@simon-shapiro.org> In-Reply-To: <199803031813.TAA01249@yedi.iaf.nl>
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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... ... ---------- 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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