Anaconda, parted, and geometry

[Alan Cox]

On Thu, Nov 06, 2008 at 09:19:05PM -0500, Chuck Anderson wrote:
> For example, Anaconda/parted likes to force cylinder alignment.  
> Windows uses the BIOS/partition table geometry which may have a 
> different idea about where cylinders begin and end.  The reasons for 
> these behaviors aren't entirely clear to me.

Last time I tried to work this out it seemed from testing things that
the policy everyone was using was:

	If there is a MSDOS partition table on the disk believe it
	Ask the BIOS
	Ask the Disk
	Follow the geometry faking 'standard'

> What to do about it?  Can't we all agree to use the same geometry when 
> dealing with the partition table?  When Anaconda/parted reads the 
> table, shouldn't it deduce the most fitting C,H,S values to use for 
> cylinder alignment and writing out new entries?  Or shouldn't it ask 
> the BIOS what to use, since that seems to be what Windows does?

The BIOS rarely knows. There are entries for the first two or sometimes first
four bios disks. Trying to make the disks to the bios numbers requires a Ph.D
in DOS arcana and BIOS extensions and then is a bit variable.

Note btw the rules have also just changed again. Some new drives use larger
physical than logical sectors so for performance you must keep logical/physical
sector alignment (so a 4K ext3 block lands on a 4K physical block etc)