Re: CFR: backup GPT header support in pmbr and loader(8) (Re: Handbook mirroring section)

From: Andrey V. Elsukov <bu7cher_at_yandex.ru>
Date: Thu, 14 Jun 2012 20:49:32 +0400
On 14.06.2012 20:05, Olivier Smedts wrote:
>> gpart(8) works only when GPT's geom exists, when PMBR is damaged
>> GEOM_PART_GPT can't detect GPT and thus you can't use it.
> 
> IMO, GEOM_PART_GPT should not depend on the MBR do detect GPT. That's
> the problem which should be fixed ; adding a partition to the MBR is
> only a workaround (and what would happen if the sector 0 was
> permanently damaged on disk ?). Why does GEOM_PART_GPT depends on the
> sector LBA 0 while the GPT header is located at sector LBA 1 ? Don't
> know the feasability of this, just saying... :-)

When the GPT disk layout is used the disk should contain a Protective
MBR at the LBA 0. This is by the UEFI standard. The protective MBR
contains one partition record with the type 0xEE, this partition covers
the entire space on the disk after the PMBR. The remaining partition
records shall each be set to zeros. When the disk capacity exceeds LBA
0xFFFFFFFF this value is used in the size field of PMBR record.

-- 
WBR, Andrey V. Elsukov


Received on Thu Jun 14 2012 - 14:49:36 UTC

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