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 <[EMAIL PROTECTED]> www.followers.net - Makers of “Elite Content Management System” View samples of Elite CMS in action by visiting http://www.followers.net/portfolio/ ---------------------------(end of broadcast)--------------------------- TIP 4: Don't 'kill -9' the postmaster