From owner-freebsd-hackers@freebsd.org  Tue Jan 31 15:43:20 2017
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From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net>
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Subject: Re: How to safely remove rest of GTP?
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To: Warren Block <wblock@wonkity.com>
Date: Tue, 31 Jan 2017 07:43:00 -0800 (PST)
CC: "Andrey V. Elsukov" <bu7cher@yandex.ru>, freebsd-hackers@freebsd.org,
 Slawa Olhovchenkov <slw@zxy.spb.ru>
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... much deleted ...
> 
> > It is impossible to have a corrupted GPT and some 
> > other type of partition table in the same time.

I believe that statement is in error.
dd if=/boot/boot0 of=/dev/ada0
Would not that lead to this very situation if done
to a GPT parted disk drive?

> Maybe when only using FreeBSD and gpart, but I'm pretty sure I've seen 
> forum users who have tried some crappy other formatting tool and have 
> overwritten the primary GPT with a valid MBR and left the secondary GPT 
> untouched.  This only becomes obvious when they bring the disk back to a 
> FreeBSD system.

As almost all MBR tools are un aware of GPT so well not do anything to
destroy the secondary GPT, so this is infact very likely to occur.


-- 
Rod Grimes                                                 rgrimes@freebsd.org