Date: Tue, 21 Jan 2003 16:52:00 -0800 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: "Andrew P. Lentvorski, Jr." <bsder@allcaps.org> Cc: Alfred Perlstein <bright@mu.org>, Dag-Erling Smorgrav <des@ofug.org>, Jeff Behl <jeff@expertcity.com>, fs@FreeBSD.ORG Subject: Re: RAID alternatives Message-ID: <20030122005200.GA9416@HAL9000.homeunix.com> In-Reply-To: <Pine.LNX.4.44.0301211550060.6477-100000@mail.allcaps.org> References: <20030121202702.GI33821@elvis.mu.org> <Pine.LNX.4.44.0301211550060.6477-100000@mail.allcaps.org>
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Thus spake Andrew P. Lentvorski, Jr. <bsder@allcaps.org>: > * Dag-Erling Smorgrav <des@ofug.org> [030121 12:04] wrote: > > > > You're right, I misread the driver source and thought it wouldn't > > attach to a 7000 or higher. > > As a side note, I don't use RAID 5 anymore, period. While RAID 10 is > wasteful, a double disk failure normally doesn't take it out. That's not > true for RAID5. > > ATA drives have gotten so crappy that I have had drive failures during the > process of rebuilding from a drive failure. Maybe we need a RAID 55 which > provides resilience against 2 drive failures ... The organization that protects against a two-disk failure is usually called RAID Level 6, actually. It is particularly useful in very large disk arrays where the probability of a two-disk failure is nonnegligible. In smaller disk arrays where high levels of reliability are required it can also be useful because drives from the same batch under similar load conditions tend to fail at about the same time, and because the additional load during recovery can cause further failures. However, the overhead is fairly high for small arrays, to the point where it often makes more sense to simply use mirroring. BTW, David Patterson has pointed out that marketing people have invented all sorts of new terms such as ``RAID 9'' (and maybe even ``RAID 55'' as you suggest) that he never coined. Maybe he should have left it at ``mirroring'', ``striping'', ``P+Q redundancy'', etc. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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