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Date:      Thu, 07 Jun 2012 11:17:07 +0400
From:      "Andrey V. Elsukov" <ae@FreeBSD.org>
To:        Hiroki Sato <hrs@FreeBSD.org>
Cc:        doc@FreeBSD.org
Subject:   Re: Handbook mirroring section
Message-ID:  <4FD05573.70801@FreeBSD.org>
In-Reply-To: <20120606.200735.1551208261335301113.hrs@allbsd.org>
References:  <alpine.BSF.2.00.1206052220390.10777@wonkity.com> <20120606.185023.497714372668376681.hrs@allbsd.org> <4FCF3021.5070802@FreeBSD.org> <20120606.200735.1551208261335301113.hrs@allbsd.org>

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On 06.06.2012 15:07, Hiroki Sato wrote:
> ae> 1. When geom_mirror module is not loaded GEOM_PART will complain th=
at the
> ae> backup GPT header is not in the last LBA and partition table will b=
e marked
> ae> as CORRUPT. The recover operation will destroy the GEOM_MIRROR's me=
tadata.
> ae>
> ae> 2. If primary GPT header or table become damaged, then gptboot will=
 not
> ae> detect GPT because the backup GPT header is not in the last LBA. So=
, the
> ae> system will not boot.
>=20
>  Thanks, I see.  Do you think the attached patch is too aggressive for
>  the problem 2?  The value of altlba should be matched with one in the
>  original secondary header when the primary header is corrupted and
>  the secondary header is looked up in this way.

Yes, i also have thought about this and this should work for most GEOM cl=
asses,
but i revised again PMBR code and it seems that it will not work anyway :=
)
Our PMBR doesn't use backup GPT header and table, and it doesn't verify
correctness of primary GPT.

=46rom the other side, there are three situations when we use GPT:
1. FreeBSD is only one system on the disk and we use PMBR and gptboot to =
boot it.

In case if we will fix PMBR your patch will help.

2. FreeBSD is no one on the disk, but we still use legacy boot method (PM=
BR+gptboot).

I don't know what behavior have other systems when they detect invalid GP=
T (i.e.
when backup header is not in the last LBA).

3. We use UEFI (it is not work yet).

Also i don't know what UEFI firmware will do with invalid GPT.

--=20
WBR, Andrey V. Elsukov


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