GPT Question

[Ian Smith]

In freebsd-questions Digest, Vol 336, Issue 9, Message: 23
On Thu, 11 Nov 2010 17:45:19 -0600 Derek Funk <dfunk6 at cox.net> wrote:
 > On 11/10/2010 9:34 PM, Mark Caudill wrote:
[..]
 > > just ran `dd if=/dev/zero of=/dev/ad12 bs=512` and let it run. That must
 > > have done the trick because I was then able to partition the disk in
 > > sysinstall and all is well. What I'm wondering is what really went on
 > > here? I'm not clear at all as to why FreeBSD (or some mechanism within
 > > this installation) isn't able to handle this. Or was this a GPT issue at
 > > all? I'd like to find out what was going on so that I don't chase my
 > > tail again on issues like this in the future. Thanks.

 > My understanding is, if you are using FreeBSD 8.x, sysinstall / fdisk 
 > will not write disk partitions.  gpart is used now.

Your understanding is incorrect.  In 8.x you MAY use gpart now, but 
sysinstall (when running as init from a booted installation medium) 
still slices and partitions disks fine, and sysinstall - or sade(8) - 
(when run as a utility from a working system) will indeed write to the 
boot sectors including MBR, and will happily slice and partition disk/s 
other than the boot slice, if and only if you have previously set sysctl 
kern.geom.debugflags=16 - not called the 'foot-shooting' bit for nothing 
- so don't forget to set it back to 0 when you've finished.

cheers, Ian