Disk Geometry

Jerry McAllister jerrymc at msu.edu
Thu Feb 28 15:40:14 UTC 2008

On Thu, Feb 28, 2008 at 12:48:37AM +0100, ras bsd wrote:

> Hello list, this is my first post here.
> My problem is:
> I've installed the OS in my laptop in this order, Win XP and Debian
> GNU/Linux. I'm trying to dive into the freebsd world from many years
> in GNU/Linux. When i start the installation, when i have to enter in
> the disk partition section an error appears saying that the disk
> geometry is not valid and, anyway, I can not see the free disk space
> that i left free after the other OS. My scope is keep working the
> three OS.
> How can i know the correct disk geometry? What am i doing wrong?

Well, I don't know why it does not see the free space unless you 
are looking in the wrong step.   There is often confusion by new
users who come from the MS world because FreeBSD uses the term 'slice'
and MS uses the term 'primary partition' to refer to the same thing.
Due to ancient conventions in Bios and etc, there can be up to 4 slices
(or primary partitions) on any physical disk.   

Lunix has its own notion of extended partition as well.  Don't try
to use that for FreeBSD.

FreeBSD must be installed/built in a free slice (primary partition by
MS vocabulary).   It cannot be put in some extended partition space.

It is possible that you have already used up the 4 slices if the laptop 
manufacturer put a diagnostic utility slice on the drive.  That is 
normally hidden from MS, but will show up to FreeBSD.  If that is true, 
and you have used up the number of slices, then FreeBSD will not allow 
you to add any.  You will need to use a tool such as 'gparted'  or 
Partition Magic to shuffle things around and maybe squeeze the other
slices and even nuke one.

Then FreeBSD uses the term 'partition' to refer to the subdivisions
of a slice.  MS has some things called extended partitions which are
not the same thing at all.

Anyway, the point where you first need to see the free space is in
the step dealing with the slices which is done with fdisk(8).

As for the disk geometry issue, it normally does not matter.  That
is the BIOS complaining.   You want to just let it go ahead and 
build things and try to ignore that error message.   Once it gets 
past loading the boot sector from a slice, FreeBSD no longer used 
the BIOS.   It handles everything itself.

There are exceptions to this response, but go ahead (once you get the
free space issue figured out) and try it and see if it works.  It
won't hurt anything and if it works, you're home free.  If it doesn't
then you have some more exploring to do.    I am not quite sure what
because although I have frequently seen that message - almost all 
the time, I have never had it not work to just go ahead and slice,
partition and build and ignore the message.  That is with both IDE(SATA)
and SCSI(SAS).

So, your real problem is finding that elusive free slice space or
freeing up a slice number to use for it.

Good luck,

> Mi laptop is Intel Core2 Duo and the Hard Disk is SATA 200 Gb Toshiba
> MK2035GSS-(S1).
> Thank you.
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