Date: Fri, 01 Feb 2002 10:31:38 +0000 From: Nick Barnes <Nick.Barnes@pobox.com> To: Erik Trulsson <ertr1013@student.uu.se> Cc: FreeBSD Stable <fbsdstable@cobble.capnet.state.tx.us>, freebsd-stable@FreeBSD.ORG Subject: Re: Setting drive geometry, big drives? Message-ID: <29589.1012559498@thrush.ravenbrook.com> In-Reply-To: Message from Erik Trulsson <ertr1013@student.uu.se> of "Fri, 01 Feb 2002 01:18:13 %2B0100." <20020201001811.GA2579@student.uu.se>
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At 2002-02-01 00:18:13+0000, Erik Trulsson writes:
> On Thu, Jan 31, 2002 at 05:51:11PM -0600, FreeBSD Stable wrote:
> > [I sent a similar message a few days ago, but that message
> > apparently got drowned in a flood of messages on another topic.]
> >
> > I have an IBM Deskstar 60GB that the BIOS reports as 29437/16/255.
> > The startup probe reports 119150/16/63. When I try to configure
> > the drive, I get a message saying 119150/16/63 is incorrect, and
> > that I need to set it to the BIOS numbers. If I set it to the
> > BIOS numbers, it still complains that it is incorrect. There is
> > a message in there warning me not to set the drive to its physical
> > geometry, though the BIOS 29437/16/255 seems a likely physical
> > geometry.
> >
> > So the partition editor picks another default, which is
> > 7476/255/63. Which seems to work fine, but now I have three
> > different numbers. The boot still shows 119150/16/63, the BIOS
> > still shows 29437/16/255, and the disklabel shows 7476/255/63.
>
> I can almost guarantee that none of those numbers are anything even
> close to the actual physical geometry of the disk.
> The numbers reported are just a convenient fiction to fit the actual
> geometry into the restrictions of the BIOS interface.
>
> (For example, very few disk today have more than 4 heads and most have
> only 2. (Unlike the 16/255 heads the numbers above indicate.))
The drive in question (a 60GB IBM Deskstar 60GXP) has 3 disks and 6
heads.
However, you are quite right that these triplets do not represent a
physical geometry. No modern disk drive can have its geometry
represented by a triplet of numbers. They have a number of concentric
"recording zones"; within each zone there is a fixed number of sectors
per track (more sectors in the outer zones because the length of each
track is greater). This 60GXP has 18 such zones. The outermost zone
has 2700 cylinders, with 780 sectors per track. The innermost zone
has 1735 cylinders with 373 sectors per track. There are 33734
cylinders in all.
Incidentally, the innermost zone includes 400 "spare" cylinders. This
is 458 MB of sectors automatically assigned by the disk to replace
defective sectors. The replacement ("defect flagging") is done during
the "Format Process" in manufacturing, and continues automatically
during use.
These triplets are just fictions of the BIOS and the ATA protocol.
The restrictions of the BIOS and of the ATA protocol are different,
which is why they come up with different fictions. If you wanted to
represent the actual physical geometry of this disk with triplets,
you'd need 18 separate triplets (one per zone).
<http://www.storage.ibm.com/hdd/support/prodspec/d60gxp_sp.pdf>;
Nick Barnes
Ravenbrook Limited
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