gpart usage

[Victor Balada Diaz]

On Tue, May 24, 2011 at 08:05:15PM +0400, Andrey V. Elsukov wrote:
> On 24.05.2011 19:09, Victor Balada Diaz wrote:
> > On Tue, May 24, 2011 at 06:46:01PM +0400, Andrey V. Elsukov wrote:
> >> On 24.05.2011 17:20, Victor Balada Diaz wrote:
> >>> also, how do i know about offsets each partitioning scheme needs? shouldn't GEOM
> >>> take care of it without user needing to know anything about it?
> >>
> >> Usually you do not need to know anything about offsets.
> > 
> > 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?

If i understood it correctly, it would be like:

Sector 0: usual IBM-PC MBR, MBR provider doesn't need anything more
Sector 1-63: Reserved by MBR scheme (dunno why, but seems to be the case, probably CHS alignment) start: 63
Sector 64: BSD scheme unused because on disk metadata is stored on second sector
Sector 65: BSD scheme (disklabel) on disk data (148 + 8 * 16 = 276 bytes according to sys/disklabel.h)
Sectors 65-81: Reserved by ??? for /boot/boot
Sectors 82+: UFS/other FS data

Is this right or i'm mistaken?

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