Date: Wed, 05 Jul 2006 17:58:48 -0400 From: Mike Jakubik <mikej@rogers.com> To: "R. B. Riddick" <arne_woerner@yahoo.com> Cc: freebsd-geom@freebsd.org Subject: Re: new class / geom_cache / request for comments Message-ID: <44AC3618.80600@rogers.com> In-Reply-To: <20060705211453.47043.qmail@web30308.mail.mud.yahoo.com> References: <20060705211453.47043.qmail@web30308.mail.mud.yahoo.com>
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R. B. Riddick wrote: > Yes, I think so... > But geom_cache is just useful, when file system's buffer cache cannot help. > > E. g.: > A degraded RAID5 on 4 consumers (3 good plus 1 failed). > When we want to get a data block, that resides on the failed consumer, we have > to read all corresponding blocks (2+1) in order to rebuild the missing block. > When we do a sequential read, we would have to read the consumers, that hold > the data blocks twice (2 x 2). > So the geom_cache could help here (2+1 real reads plus 2 from the cache), if > the provider is not too busy. > Wouldn't it make more sense to modify geom_raid5 to include this behavior, instead of writing a new and separate geom class that has only one useful function?
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