1 processor vs. 2

[Charles Swiger]

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