Re: Performance problem - reads slower than writes

Brian Candler
2012-02-03T22:10:19Z

On Fri, Feb 03, 2012 at 01:42:54PM -0600, Stan Hoeppner wrote:
> You've hit the peak read rate of these Hitachi drives. As others
> pointed out, if you need more read performance than the dozen of these
> you plan to RAID stripe, then you'll need to swap them for units with a
> faster spindle:
>
> 7.2k 1.21x
> 10k 1.68x
> 15k 2.53x
>
> or with SSDs, which will yield an order of magnitude increase. Your
> stated need is 20M 500-800KB files, or 20GB if my math is correct.

Thanks for your suggestion, but unfortunately your maths isn't correct: 20M
x 0.65MB = 13TB. And that's just one of many possible datasets like this.

I'm aware that I'm working with low-performance drives. This is intentional:
we need low power consumption so we can get lots in a rack, and large
capacity at low cost.

Fortunately our workload will also parallelise easily, and throwing it
across 24 spindles will be fine. But obviously I want to squeeze the most
performance out of each spindle we have first. I'm very happy to have found
the bottleneck that was troubling me :-)

Regards,

Brian.