GPT as default?

Marcel Moolenaar xcllnt at
Fri Apr 20 17:36:35 UTC 2007

On Apr 20, 2007, at 10:15 AM, Dag-Erling Smørgrav wrote:

> Ivan Voras <ivoras at> writes:
>> Many systems (including MacOS X and Solaris) are moving to GPT
>> partitions (,  
>> mostly
>> because they don't have the above limitations. My proposal is that we
>> deprecate BSD labels and move to GPT in 7.0 (or more correctly, if  
>> the
>> stars were to be benevolent on us, on the new systems that are
>> installed by the new GPT-aware installer :) ).
> Not unless geom_gpt receives considerable attention.

It receives attention.

> Currently, it is not even possible to list the GPT, let alone create
> new partitions, if one of the partitions is open.  GPT can not be the
> default partitioning scheme until this is addressed.

You can list with the -r option. You cannot create unless you allow
foot-shooting in GEOM (i.e. set kern.geom.debugflags=16). The latter
a known side-effect of GEOM and has nothing to do with GPT itself.

Anyway: The new G_PART class is there to fix it...

>> The second is more serious: FreeBSD boot code cannot boot from a GPT
>> partition.
>> Part of the problem is that GPT uses GUIDs for distinguishing
>> partition types, so the current code that recognizes various  
>> partition
>> types (Linux, FreeBSD, NTFS - the famous "F1" prompt) may need to be
>> thrown out since each GUID is 16 bytes long and AFAIK there's only
>> about 300 bytes in the MBR for the boot code.
> DOS partitions normally start on a cylinder boundary, even though
> cylinders no longer mean anything.  This means there is plenty of
> space for code and data between the MBR and the first partition.
> I don't know if this is also the case with GPT.

It isn't. If disk space is needed, one can always create a partition
for it. There's no need to stuff things in anonymous sectors.

Marcel Moolenaar
xcllnt at

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