On 02/06/2009 20:47, Keld Jørn Simonsen wrote:
[...]
My perception is that raid10,f2 is probably the fastest also for small random
reads because of the lower latency, and faster transfer times due to only
using the outer disk sectors. For writes the elevator evens out the
ramdom access. Benchmarks may not show this effect as they are often
done on clean file systems, where the files are allocated in the
beginning of the fs.
For cases where you need cheap disk space, and have big files like
.iso's then raid5 could be a good choice because it has the most space
while maintaining fair to good performance for big files.
In your case, using 3 disks, raid5 should give about 210 % of the nominal
single disk speed for big file reads, and maybe 180 % for big file
writes. raid10,f2 should give about 290 % for big file reads and 140%
for big file writes. Random reads should be about the same for raid5 and
raid10,f2 - raid10,f2 maybe 15 % faster, while random writes should be
mediocre for raid5, and good for raid10,f2.
I'd be interested in reading about where you got these figures from
and/or the rationale behind them; I'd have guessed differently...
Cheers,
John.
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