Adding hard disks

Overriding the root disk geometry stored in the BIOS

At boot time you can override the geometry information that the BIOS stores about the root disk using the biosgeom bootstring:

defbootstr biosgeom=(cylinders,heads,sectors)

This bootstring passes your definition of the disk's geometry (number of cylinders, heads, and sectors) to the hard disk device driver (rather than using the values stored in the BIOS). It does not change the disk geometry defined in the BIOS (either unextended or extended).

You may need to use the biosgeom bootstring to override the geometry defined for large SCSI disks when used with host adapters which assume a standard disk geometry. If you do not redefine the geometry passed to the device driver, the values defined for the number of heads and sectors in the BIOS of the host adapter may imply that the disk has more than 1024 cylinders. See ``BIOS support for disks larger than 1024 cylinders'' for more information.

To find out the current numbers defined for the disk's cylinders, heads, and sectors, enter the biosgeom command at the boot prompt.

Once the disk geometry has been redefined in this way, you can boot the SCO OpenServer system or any other operating system on the root disk using the bootos(HW) command from the boot prompt.

To add this geometry definition to the default bootstring, edit the definition of DEFBOOTSTR in /etc/default/boot. For example:

   DEFBOOTSTR=hd(40)biosgeom unix=(255,255,63)
Alternatively, if the BIOS defines the disk as having less than 1024 cylinders, or the boot filesystem and all other operating system partitions lie within the first 1024 cylinders, you can redefine the disk geometry stored in the masterboot block on the disk as described in ``Writing a new masterboot block''.
Next topic: Writing a new masterboot block
Previous topic: Defining IDE and ESDI disk geometry in the BIOS

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003