FreeBSD, 160GB HD, and a Bios limitation

CyberLeo Kitsana cyberleo at
Wed Nov 21 04:31:45 PST 2007

Christoper Tucker wrote:
> I used the "all" command here. Using the Seagate utility, the drive had
> earlier been set to 160GB, yet the installer sees 120GB here, it seems.

The IDE interface that the drive is connected to does not support LBA48
addressing, and thus can only address 2^28 sectors, or about 120GiB. As
the higher sectors cannot be addressed, they essentially do not exist.
I'm doubtful there are any software workarounds for this issue.

As for the size reported in the BIOS, that's only required to get the
system booted, and all boot files must reside within that space. Once
the FreeBSD kernel takes over, it communicates with the IDE interface
directly, and is not subject to BIOS limitations.

The biggest concern is that, when the boot sector and partition
information is written, the geometry fdisk uses must match that which
the BIOS expects. If not, it's possible that the bootloader, which must
use BIOS calls to access the disk, will end up looking in the wrong places.

It might be easier to simply procure a cheap, recent Promise or similar
bootable PCI IDE adapter, which will not suffer these limitations, and
will likely be faster than the onboard adapter.

Fuzzy love,
Technical Administrator
CyberLeo.Net Webhosting
<CyberLeo at CyberLeo.Net>

Furry Peace! -

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