svn commit: r216269 - head/sys/geom/part

Bruce Cran bruce at
Fri Dec 10 08:52:38 UTC 2010

On Fri, 10 Dec 2010 02:00:23 +0100
Erik Trulsson <ertr1013 at> wrote:

> Modern drives do not really report 'the current CHS geometry'. They
> report a fake geometry that normally do not have anything do with the
> actual geometry.  (As an example just about all modern ATA/SATA drives
> report having 16 heads, while in reality none of them have more than
> 10 heads and most of them have fewer heads than that.)

Note that I said 'current', not 'correct' :)
They do continue to report the current CHS geometry that the BIOS has
configured: for example overriding the settings to use a setting of 8H
instead of 16H in the BIOS does get detected by FreeBSD when it reads
the 'current CHS geometry' fields.  And yes, the only thing that's
useful for nowadays is configuring the MBR or BSD disklabel.

Bruce Cran

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