fdisk(8) vs gpart(8), and gnop

[Warren Block]

On Sun, 1 Jun 2014, Ian Lepore wrote:

> On Sat, 2014-05-31 at 19:00 -0700, John-Mark Gurney wrote:
>> Michael W. Lucas wrote this message on Sat, May 31, 2014 at 20:42 -0400:
>>> $SUBJECT have been two contentious points of discussion in private
>>> mail, Twitter, the BSDCan bar track, and random people passing on the
>>> street. I was very surprised at the number of knowledgeable people who
>>> have different ideas on this and argue about it at length.
>>>
>>> I'm hoping to verify what seems to be correct.
>>>
>>> First, is fdisk EVER necessary? I *believe* that gpart's '-a 4k'
>>> handles all alignment issues for the 512B/4KB sector issues. If you
>>
>> gpart's -a will not properly align MBR's slices due to enforced CHS...
>
> Maybe this is naive, but... can't we just *fix* that?

Thread starts here:
http://lists.freebsd.org/pipermail/freebsd-geom/2014-February/005835.html

> For the longest time geom would warn about "geometry does not match
> label" that had something to do with different parts of the code
> calculating different CHS values.  Eventually it was decided to remove
> the unactionable message, and my vague memory is that the justification
> was basically "because CHS is meaningless to geom and modern BIOSen."
>
> If there's some "it would cause problems on this ancient hardware that
> only 3 people in the world use" (I'm usually one of those people -- we
> support some old equipment in the field at $work), then maybe there
> could be a flag that enables the old CHS alignment behavior.

Short form of above: gpart is supposed to hide and handle underlying 
GEOM issues, so it needs an override to be able to create these 
"non-standard" MBRs with slices aligned to arbitrary values.