Re: How to improve db performance with $7K?

William Yu <wyu(at)talisys(dot)com> writes:

> Using the above prices for a fixed budget for RAID-10, you could get:
>
> SATA 7200 -- 680MB per $1000
> SATA 10K -- 200MB per $1000
> SCSI 10K -- 125MB per $1000

What a lot of these analyses miss is that cheaper == faster because cheaper
means you can buy more spindles for the same price. I'm assuming you picked
equal sized drives to compare so that 200MB/$1000 for SATA is almost twice as
many spindles as the 125MB/$1000. That means it would have almost double the
bandwidth. And the 7200 RPM case would have more than 5x the bandwidth.

While 10k RPM drives have lower seek times, and SCSI drives have a natural
seek time advantage, under load a RAID array with fewer spindles will start
hitting contention sooner which results into higher latency. If the controller
works well the larger SATA arrays above should be able to maintain their
mediocre latency much better under load than the SCSI array with fewer drives
would maintain its low latency response time despite its drives' lower average
seek time.

--
greg