Date: Wed, 3 Mar 2004 17:47:29 -0500 From: Charles Swiger <cswiger@mac.com> To: Reko Turja <ignatz@liukuma.net> Cc: 'Free BSD Questions list' <freebsd-questions@freebsd.org> Subject: Re: 1 processor vs. 2 Message-ID: <BFFA41A5-6D64-11D8-85AD-003065ABFD92@mac.com> In-Reply-To: <000601c4016d$cdb571e0$0a06a8c0@rekon> References: <000601c4016d$cdb571e0$0a06a8c0@rekon>
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On Mar 3, 2004, at 5:20 PM, Reko Turja wrote: >> RAID-1 will be about 50% faster than RAID-5 doing reads regardless of >> size, and will also be *much* faster doing small writes-- by a factor >> of 4, perhaps. > > The abovementioned figures seem more like comparing RAID-0 (striping) > to RAID-5 (striping with ECC) than RAID-5 to RAID-1 (mirroring). In > my experience mirroring is always the slowest RAID in terms of > retrieving data, writes might be quite comparable with RAID-1 and > RAID-5 though. Your mileage may vary. :-) However, consider that RAID-1 (mirroring) read performance should always be better than RAID-0 (striping) because you can get the data you want using a single read from either device regardless of size, and you can do things like distribute reads geometrically to reduce head motion for the RAID-1 case-- whereas with reads above the stripe size, the RAID-0 case requires you to access both devices and glue the results together. -- -Chuck
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