Re: RAID arrays and performance

On Tue, 29 Jan 2008, Gregory Stark wrote:
>> This was with 8192 random requests of size 8192 bytes from an 80GB test file.
>> Unsorted requests ranged from 1.8 MB/s with no prefetching to 28MB/s with lots
>> of prefetching. Sorted requests went from 2.4MB/s to 38MB/s. That's almost
>> exactly 16x improvement for both, and this is top of the line hardware.
>
> Neat. The curves look very similar to mine. I also like that with your
> hardware the benefit maxes out at pretty much exactly where I had
> mathematically predicted they would ((stripe size)^2 / 2).

Why would that be the case? Does that mean that we can select a stripe
size of 100GB and get massive performance improvements? Doesn't seem
logical to me. To me, it maxes out at 16x speed because there are 16
discs.

Amusingly, there appears to be a spam filter preventing my message (with
its image) getting through to the performance mailing list.

Matthew