> Theory vs. real life. In Theory, RAID5 is faster because less
> data have
> to be written to disk. But it's true, many RAID5 controllers
> don't have
> enough CPU power.
I think it might not be just CPU-power of the controller. For RAID0+1
you just have two disc-I/O per write-access: writing to the original set
and the mirror-set. For RAID5 you have three additional
disc-I/O-processes: 1. Read the original data block, 2. read the parity
block (and calculate the new parity block, which is not a disk I/O), 3.
write the updated data block and 4. write the updated parity block. Thus
recommendations by IBM for DB/2 and several Oracle-consultants state
that RAID5 is the best compromise for storage vs. transaction speed, but
if your main concern is the latter, you're always best of with RAID0+1;
RAID0+1 does indeed always and reproducably have better write
performance that RAID0+1 and read-performance is almost always also
slightly better.
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