Fdisk disagreas with BIOS over 120GB drive.

Siegbert Baude Siegbert.Baude at gmx.de
Tue Aug 19 08:30:53 PDT 2003


>>Fdisk (using /stand/sysinstall) disagrees with the values my bios is 
>>reporting.  My BIOS reports that my 120GB drive has this geometry: 59131 
>>Cylendars, 16 Heads, and 255 sectors.  The drive is an IBM deskstar.  When i 
>>try to enter the correct geometry, Fdisk gives me the message below. 
>I hope someone with more detailed knowledge responds as well, but my 
>experience says just take what FreeBSD's fdisk gives you.  The
>geometry on "modern" disks is virtual as far as what you are dealing
>with anyway.

The conflict probably exists between the translation detected by the 
BIOS and the partition table entries on the disk.

Will this disk be used only within FreeBSD or is it a multi-OS machine?
In the latter case it is very important, that all OSes use the same 
translation, otherwise, one could overwrite data of the other. I would 
recommend to use every OS's fdisk for its own slice in this order: Win, 
Linux, FreeBSD. Make sure Linux and FreeBSD, will use the same 
translation chosen by Windows' fdisk.

Is there already data on the disk?
If not, I would suggest to erase the partition table. CAUTION: This will 
make all data on your disk disappear!

dd if=/dev/zero of=/dev/ad2 count=1 bs=512

Then reboot and let the BIOS autodetect. Normally there will be modes 
detected with either 16/63 or 255/63 H/S. The former allows for some 
megabytes less wasted space at the end of the disk.
If you use FreeBSD fdisk now, it should allow the values of the BIOS 
without protest.

Another approach after having erased the partition table would be to 
check in dmesg, which CHS values are read by FreeBSD out of the disk. 
Then try to manually give this values to your BIOS.



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