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

On 4/14/05, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> That's basically what it comes down to: SCSI lets the disk drive itself
> do the low-level I/O scheduling whereas the ATA spec prevents the drive
> from doing so (unless it cheats, ie, caches writes).  Also, in SCSI it's
> possible for the drive to rearrange reads as well as writes --- which
> AFAICS is just not possible in ATA.  (Maybe in the newest spec...)
>
> The reason this is so much more of a win than it was when ATA was
> designed is that in modern drives the kernel has very little clue about
> the physical geometry of the disk.  Variable-size tracks, bad-block
> sparing, and stuff like that make for a very hard-to-predict mapping
> from linear sector addresses to actual disk locations.  Combine that
> with the fact that the drive controller can be much smarter than it was
> twenty years ago, and you can see that the case for doing I/O scheduling
> in the kernel and not in the drive is pretty weak.
>
>

So if you all were going to choose between two hard drives where:
drive A has capacity C and spins at 15K rpms, and
drive B has capacity 2 x C and spins at 10K rpms and
all other features are the same, the price is the same and C is enough
disk space which would you choose?

I've noticed that on IDE drives, as the capacity increases the data
density increases and there is a pereceived (I've not measured it)
performance increase.

Would the increased data density of the higher capacity drive be of
greater benefit than the faster spindle speed of drive A?

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