linux-kernel - Re: Disk geometry from /sys

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Date:	Wed, 9 Apr 2008 22:52:07 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
Cc:	Francis Moreau <francis.moro@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Disk geometry from /sys

> Why do you want to know what cylinder size the hard disk pretents to
> have?  What use could it be?  Harddisks have varying numbers of sectors

It matters on a CHS addressed device - vaguely.

> drive.  All that matters on a modern drive is the total number of
> sectors since all access is done by requesting a specific sector number
> starting from the begining of the drive.  Where it is physically located
> is none of software's business, and it may not even be adjacent to the
> sector with a number right next to the requested one due to defect
> management and various optimizations.

And some other OS's make certain assumptions about layout that must agree
with that OS view of the disk. A good general rule is to believe the
partition table information if present and if not use SG_IO to issue an
IDENTIFY to any ATA or CFA drive to see how it has mapped the device.

Even better make use fo the existing tools whenever possible - disk
partitioning is more like magic than science

Alan
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