Re: [PATCH] pdcraid and weird IDE geometry

From: Andries Brouwer <aebr@win.tue.nl>
To: Jeff Garzik <jgarzik@pobox.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Walt H <waltabbyh@comcast.net>,
	arjanv@redhat.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	davzaffiro@tasking.nl
Subject: Re: [PATCH] pdcraid and weird IDE geometry
Date: Thu, 17 Jul 2003 18:03:28 +0200	[thread overview]
Message-ID: <20030717180328.A2467@pclin040.win.tue.nl> (raw)
In-Reply-To: <3F16C1F3.40206@pobox.com>; from jgarzik@pobox.com on Thu, Jul 17, 2003 at 11:34:11AM -0400

On Thu, Jul 17, 2003 at 11:34:11AM -0400, Jeff Garzik wrote:

> Can't you fix the geometry from fdisk expert mode?
> 
> I've done that several times before, when otherwise like-sized disks 
> appeared with vastly different geometry.

It is easiest to think that it is meaningless what you say
(in this case). A disk does not have a geometry, and
moreover you cannot change it with fdisk.

However, under some circumstances, some kernels will guess
a (translated) geometry from a DOS-type partition table,
so it is true that under some kernel versions you can use
fdisk to change the kernel's ideas about disk geometry.
A very fragile activity.

[Moreover, there are several kinds of geometry, and the present
authors of ide-disk.c conveniently confused them all.
Concerning pdcraid, I don't know for which of the possible
ideas of geometry it is true that one needs the first sector
of the last cylinder.]

Andries