Re: gpart, bsdlabel and fdisk

On Thu, 2009-10-22 at 12:29 +1100, Aristedes Maniatis wrote:
> On 22/10/09 12:16 PM, Robert Noland wrote:
> > gpart create -s GPT<disk>
> 
> Sorry to keep asking so many questions, but hopefully this is all helpful to everyone else moving to the new gpart tools.
> 
> I can see there are three common partition types now in use on FreeBSD: MBR, BSD and GPT. I assume MBR is the same type sysinstall offerred FreeBSD users up until now for bootable disks. And GPT is the new type which is needed to support booting into ZFS. Does this explain why bsdlabel shows odd results for our GPT partitioned disks: it doesn't have support for GPT?
> 
> I don't understand this in the gpart manual:
> 
>     "The GEOM_PART_GPT option adds support for the GUID Partition Table (GPT) found on Intel Itanium computers and Intel-based Macintosh computers."
> 
> Why is GPT restricted to use on Macs and Itanium? As long as BIOS is able to load the boot sectors, shouldn't it work everywhere? Can you clarify this a little?
> 
> Will GPT be the default recommended partition type for all FreeBSD users now? Are there downsides to using it? Does it have a documentation page somewhere?

Well now... You probably want to wikipedia some of this....
http://en.wikipedia.org/wiki/Partition_%28computing%29 is probably a
good starting place.  GPT is the easiest way to get zfs working.  With
GPT you write a PMBR (protective master boot record) to sector 0 of the
drive.  This prevents (should prevent) older tools that don't understand
GPT from messing with the disk.  Basically it shows the disk as having a
single partition which encompasses the disk.  The GPT header then
occupies the second sector on the disk, followed by the partition
entries.

As I understand it (never actually tried it), Windows XP/Vista
whatever... Don't understand GPT yet, so you can't really dual boot with
it.  For that you probably still need an MBR scheme.  But I haven't run
into any pc systems that won't handle GPT yet, other than one of them
needing the active flag set in the PMBR.

robert.

> Thanks
> 
> Ari Maniatis
> 
-- 
Robert Noland <rnoland_at_FreeBSD.org>
FreeBSD