Re: NetBSD file system chat

On Wed, 13 Jul 2005, Mike Cheponis wrote:

> On Wed, 13 Jul 2005, James Buchanan wrote:
>
>> Since we can't know the physical disk geometry on modern disks,
>
> I don't believe this is true.
>
> If one were willing to measure transfer rates for a variety of sectors, I 
> suspect an exact map of the disk could be determined.

 	Useful reference for this:

 	http://www.pdl.cmu.edu/PDL-FTP/DriveChar/traxtent.pdf

 	    Track-aligned extents (traxtents) utilize disk-specific
 	    knowledge to match access patterns to the strengths of
 	    modern disks. By allocating and accessing related data
 	    on disk track boundaries, a system can avoid most ro-
 	    tational latency and track crossing overheads. Avoiding
 	    these overheads can increase disk access efficiency by up
 	    to 50% for mid-sized requests (100–500 KB). This paper
 	    describes traxtents, algorithms for detecting track bound-
 	    aries, and some uses of traxtents in file systems and video
 	    servers.

-- 
 		David/absolute       -- www.NetBSD.org: No hype required --