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SubjectRe: disk head scheduling
Date
In article <19990319181823.A543@anjala.mit.edu>,
Arvind Sankar <arvinds@mit.edu> wrote:
>
>IBM claims that my hard disk (Model IBM DHEA-38451) has 4 platters and 8 heads.
>I assume these are physical, since there are either 15 or 16 logical heads in
>CHS mode (settable via jumpers).

Do they claim how many sectors?

I bet they don't. A lot of the better disks split up the disk in
"regions", and have a variable number of sectors: more sectors on the
outer edge where there is more room, etc.

Density is important to modern disks, and as long as disks rotate you
will have a property where the outer tracks have more space.

Quite frankly, anybody who even _thinks_ he knows how the disk is
organized is living in the past. Give up on it, and just consider it a
linear array of sectors. Anything else just amounts to repeatedly
hitting yourself on the head with a virtual icepick, and is just about
as useful.

Just say no to unnecessary complexity that just doesn't buy you
anything. Linux uses a one-way scheduler for many good reasons, not the
least of which are that it is fair and that it is simple.

The same goes for filesystems: trying to optimize the filesystem for
some random number of sectors per track is just stupid these days.

Linus

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