On 4/14/05, Tom Lane <[EMAIL PROTECTED]> 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?

Matthew Nuzum

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