On Aug 14, 2009, at 9:22 PM, Robert Nichols
<rnicholsNOSPAM@xxxxxxxxxxx> wrote:
> Ross Walker wrote:
>> On Aug 14, 2009, at 12:48 PM, Robert Nichols
>> <rnicholsNOSPAM@xxxxxxxxxxx> wrote:
>>
>>> Ross Walker wrote:
>>>> On Fri, Aug 14, 2009 at 5:00 AM, Chan Chung Hang
>>>> Christopher<christopher.chan@xxxxxxxxxxxxxxx> wrote:
>>>>
>>>> Question now is, was the first sector of partition 1 damaged (was
>>>> it
>>>> 63 or 64 sectors dd'd)?
>>>>
>>>> If so it will require a more tricky procedure to fix.
>>> No, the ext2 file system does not use the first 1K block of the
>>> partition.
>>> That space is left free for a boot loader. The first super block
>>> of the
>>> file system is the 2nd 1K block of the partition, and even if that
>>> gets
>>> overwritten it is easily recovered from one of the backup super
>>> blocks.
>>
>> I did not know that, good information.
>>
>> So stage2 is written in first 1k of the partition?
>
> No, nowhere near enough room. Just stage 1 goes into the first
> sector.
> The second sector is unused. Stage 1 then loads the fs-specific
> stage 1.5
> from absolute sector numbers on the disk. Stage 1.5 then loads
> stage 2
> from the file system. (Yes, if the *_stage1_5 files get moved on the
> disk, you have to re-run the GRUB installer.)
>
> The only time more than the 446-byte stage 1 gets installed is when
> installing GRUB in the MBR or in the boot sector of a logical drive in
> the extended partition. There, there can be a full track available,
> which is enough room for the appropriate stage 1.5, but not for the
> 100+ KB of stage 2.
>
>> Ah but I believe the OP has the partition setup as a LVM PV. Question
>> is does LVM leave the first 1k free for a stage2 boot loader?
>>
>> And if the LVM metadata is corrupt is there a second copy at the end
>> of the PV?
>
> No idea. I don't use LVM. Having a known recovery path if things get
> munged is more important to me than the features of LVM.
Since you don't know if LVM has a recovery path how can you imply it
doesn't?
-Ross
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