[parted-devel] > 63 heads. Why does this keep coming up?

[Curtis Gedak]

On 11-02-13 02:53 PM, Phillip Susi wrote:
> On 02/13/2011 01:28 PM, Curtis Gedak wrote:
>> It might be useful to print a message indicating a problem with invalid
>> CHS geometry, and that parted will write a geometry when edits are made
>> to the partition table.
>>
>> What are your thoughts regarding informing the user about invalid CHS?
>
> CHS is just leftover garbage from the days when dinosaurs walked the 
> earth.  Nobody actually uses it anymore, so it doesn't really matter. 
> If the existing CHS addresses are nonsense, then parted can hardly 
> make it any worse, and so no harm will come from it.  I therefore 
> don't see any reason to send the user into a panic warning them about it.

There are some old operating systems, such as DOS, that pay attention to 
the CHS values.  Today I think DOS is mainly used as a base OS for 
programs to re-flash the BIOS on a motherboard.  In these types of 
situations, I do not think multiple disk partitions are a concern.  
Hence you might be right that a warning message might cause more 
confusion than it is worth.

>
>> TEST B SUMMARY
>> --------------
>> Parted also changes the disk geometry to a valid one when a new
>> partition is created. Now that the CHS geometry has changed, fdisk no
>> longer sees the original partition as cylinder aligned. I wonder if this
>> change in geometry could possibly cause problems later on....
>
> There actually isn't anything to change since the disk geometry is not 
> stored in the partition table.  Parted just tries to guess what 
> geometry was used to compute the existing CHS addresses from their 
> LBA, and use that same geometry when it needs to compute a CHS 
> address.  If that guess fails, then I believe parted just assumes the 
> max values for heads and sectors when it has to write CHS values.

I agree that the CHS values are calculated and not actually stored in 
the MBR.  Hence fdisk must also have some sort of calculation to derive 
CHS values for a device.  Still, changing of the values would have an 
impact on some old operating systems, such as DOS.  However as stated 
above, I think DOS is mostly used in trivial situations where multiple 
disk partitions are not needed.  Also DOS would be unable to address all 
of the storage space on todays large hard disk devices.

Regards,
Curtis