Heres a reference to the track-aligned extents thing i mentioned: 
Its in the usenix FAST 2002 proceedings, entitled 'track-aligned extents: 
matching access patterns to disk drive characteristics'. it can be 
downloaded from http://www.pdl.cmu.edu/ftp/stray/traxtent_abs.html
even off-disk, it can pay off to know the geometry. 
Isildur

On Tue, 14 May 2002, Lord Isildur wrote:

> even modern scsi disks have such a concept, and they make very good use 
> of it in disk firmware when scheduling operations.. 
> and even outside of disk firware, being aware of tracks is both possible 
> and useful.. check out http://www.pdl.cmu.edu/Freeblock and 
> http://www.pdl.cmu.edu/Dixtrac.. the track-aligned extents stuff isn't online
> atm it seems.. 
> now, ide disks are _way_ worse at trying to present the disk as an 
> abstract vector of blocks with no performance impact from particular 
> access patterns... 
> Isildur
> 
> On 14 May 2002, Perry E. Metzger wrote:
> 
> > 
> > On Mon, May 13, 2002 at 11:51:52PM -0400, Lord Isildur wrote:
> > > for example, one of the very cheap things with a pretty good win is to 
> > > avoid allocating blocks which span track boundaries, as a quick way to 
> > 
> > Haven't seen a disk where you had any idea what a "track" actually was
> > in years. I suppose "Lord Isildur" doesn't know about ZBR.
> > 
> > For reference, on modern drives, "geometry" is entirely a fiction.
> > 
> > --
> > Perry E. Metzger		perry@wasabisystems.com
> > --
> > NetBSD: The right OS for your embedded design. http://www.wasabisystems.com/
> > 
>