Re: 1 processor vs. 2

From: Charles Swiger (cswiger_at_mac.com)
Date: 03/03/04

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    Date: Wed, 3 Mar 2004 17:47:29 -0500
To: Reko Turja <ignatz@liukuma.net>

    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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