Re: using GPT support in BIOS boot

["Jonathan A. Kollasch" <jakllsch%kollasch.net@localhost>]

On Fri, Jan 07, 2011 at 01:31:52AM -0800, Thomas Mueller wrote:
> Some questions on my part:
> 
> What versions of NetBSD is this good for?  Only 6 (current)?

You need gpt(8) from current to install the new mbr_gpt code.
You also need the new /boot and bootxx code.

> Would NetBSD be able to see only the first 26 partitions?  Would NetBSD 
> partitions such as /, swap, /home all be MBR partitions, or would they be 
> subpartitions as is done when using traditional fdisk on hard disks < 2 TiB?

The first-26-partitions limitation is only in boot(8),
it's due to the existing syntax used to address partitions,
for example, "hd0z:".  GPT would be better addressed with a
syntax more like "hd0-26:", or something.

The kernel's DKWEDGE_METHOD_GPT code may have a 128-partition
limitation though.

> 
> Can part of the disk < 2 TiB be reserved for OSes not aware of GPT, such as 
> FreeDOS?

There's no standardized way to do this, though Apple has a method they
use in bootcamp.
 
> How would NetBSD be installed if sysinst can't be used?  Just unpack the sets 
> over the root directory and edit some of the files under /etc?

Yeah, tar pzxf the sets, MAKEDEV all, edit fstab and rc.conf.

> Where does one get gpt and dkctl, what package do they belong to?  Or will 
> they be part of NetBSD 6 (current) and on the installation CD?

They're part of the NetBSD base system.  No idea if they're in the
INSTALL ramdisk.  Also, the new gpt(8) could be compiled for an older
release with a bit of coercion.

> I wouldn't use gpt on my present 40 GB hard disk but am planning to buy a new 
> computer with amd64 multicore CPU and possibly Western Digital's Caviar Green 
> 3 TB hard drive, not that I could use > 2 TB immediately, but to be more 
> prepared for the future.

You can convert a disk to GPT later if you leave 34 or more sectors
free at the beginning and end of the media.

> 
> I can't really see how I'd use > 26 partitions, even with FreeDOS + NetBSD + 
> FreeBSD + Linux.

Well, I've come close to running out of the 14-usable disklabel
partitions once upon a time on a NetBSD/xen dom0, I use LVM now
though.

        Jonathan Kollasch