gpart usage

[Andrey V. Elsukov]

On 24.05.2011 21:27, Victor Balada Diaz wrote:
>>> So the 16 sector offset in BSD label is really needed or isn't?
>>
>> First 8 KBytes of the freebsd partition are reserved for the boot code
>> (/boot/boot). The table of BSD partitions itself is located in the
>> second sector. So, if you plan to create freebsd-ufs partition you can
>> create it without any offset. But if it will be not an UFS partition,
>> then i would created it with offset, otherwise you can wipe the BSD label.
> 
> Who's the one reserving the 16 sector (8 KBytes) offset? the UFS filesystem? the BSD slice/disklabel
> provider? the MBR provider?

BSD slice provider.

> If i understood it correctly, it would be like:
> 
> Sector 0: usual IBM-PC MBR, MBR provider doesn't need anything more
> Sector 1-62: Reserved by MBR scheme (dunno why, but seems to be the case, probably CHS alignment) start: 63

Yes, currently we are actively discussing about this in the
freebsd-geom@ maillist.

> Sector 63: BSD scheme unused because on disk metadata is stored on second sector

Here is saved the boot1 stage of /boot/boot.

> Sector 64: BSD scheme (disklabel) on disk data (148 + 8 * 16 = 276 bytes according to sys/disklabel.h)

GEOM_PART_BSD supports up to 20 partitions.

> Sectors 65-(63+16): Reserved by ??? for /boot/boot

Here is saved the boot2 stage of /boot/boot.

> Sectors (63+16)+: partitions

If you will not use offset for the first BSD partition, then you can
wipe BSD scheme with this command:
# dd if=/dev/zero of=/dev/da0s1a count=2

-- 
WBR, Andrey V. Elsukov

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