> For example, does the total number of sectors (su) override the
> effective unit size (ns * nc * nt)?  Or, *must* they agree?

> In more practical terms, if the drive reports N sectors (and you
> *assume* this to be Gospel), *must* you define a geometry that
> coincides with this; does not *exceed* this; or, is the geometry
> largely immaterial?

I don't know about disktab specifically, since I never use disktab.
But I can say that in my experience, neither of the constraints you
mention applies to the label.

> I ask since I had problems some years ago under FreeBSD where the
> system was using a bogus geometry instead of the actual geometry.  As
> a result, the system thought the drive was bigger than it really was.
> Since my swap happened to be at the end of the drive, the problem
> would only turn up when swap was heavily used.  And, of course, this
> was not a "graceful recovery"!

I've never had such trouble, but I've always been careful that
partitions that end at the "end" of the disk always end at the actual
end, not at the end of what the label thinks is the last cylinder.
Indeed, the tool I use to repartition warns if I set a partition to end
after what the total-sector-count field says is the end of the disk.

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