Date: Mon, 2 May 2005 07:38:19 -0700 (PDT) From: Arne "Wörner" <arne_woerner@yahoo.com> To: Allen <bsdlists@rfnj.org> Cc: freebsd-performance@freebsd.org Subject: Re: Very low disk performance on 5.x Message-ID: <20050502143819.49818.qmail@web41207.mail.yahoo.com> In-Reply-To: 6667
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--- Allen <bsdlists@rfnj.org> wrote: > Scenario B, verified read enabled: > 1. RAID card reads up ALL blocks in the stripe (5 reads). > 2. RAID card pretends the block requested is on a "degraded" > drive, and > calculates it from the other 3 + the XOR stripe. > 3. RAID card reports the value back, or tosses some kind of > error. > > You can see, the cache just doesn't play a part in what I was > describing, > which is basically the array performing as though it is degraded > when in > fact it is not, to catch failures that would otherwise be > missed. > That would be a funny implementation. Step one could be done mostly from cache in case of sequential reads from a device (like /dev/ad0s1f or so). In this thread we always looked at sequential reads, as far as I recall... -Arne __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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