Re: RAID 0 not as fast as expected

Craig A. James wrote:
> I'm experiment with RAID, looking for an inexpensive way to boost
> performance.  I bought 4 Seagate 7200.9 120 GB SATA drives and two SIIG
> dual-port SATA cards.  (NB: I don't plan to run RAID 0 in production,
> probably RAID 10, so no need to comment on the failure rate of RAID 0.)
>
> I used this raw serial-speed test:
>
>   time sh -c "dd if=/dev/zero of=./bigfile bs=8k count=1000000 && sync"
>   (unmount/remount)
>   time sh -c "dd if=./bigfile of=/dev/null bs=8k count=1000000 && sync"
>
> Which showed that the RAID 0 4-disk array was almost exactly twice as
> fast as each disk individually.  I expected 4X performance for a 4-disk
> RAID 0.  My suspicion is that each of these budget SATA cards is

I am assuming linux here, Linux software raid 0 is known not to be super
duper.

Secondly remember that there is overhead involved with using raid. The
direct correlation doesn't work.

Joshua D. Drake

>


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