Re: [linux-lvm] Recovering "broken" disk ( 17th )

[Brian McCullough <bdmc@bdmcc-us.com>]

On Tue, Oct 19, 2021 at 05:06:37AM -0500, Roger Heflin wrote:
> I would edit the vgconfig you dd'ed with an editor and make sure it looks
> reasonable for what you think you had.

It turns out, comparing the information that I pulled off of the drive
with what I find in /etc/lvm/backup, that the first part of the vgconfig
information is missing.  As I said in one of my messages, the
information that I retrieved from the disk starts at 0x1200.  I don't
know whether that is correct or not.  It does not appear to be a proper
"backup" file, which I think it should be.

I rebooted ( partially ) the machine and copied the vgconfig backup file
from that, but am somewhat concerned, because I don't seem to be able to
match the UUIDs.  The one that I seem to see in the vgconfig data that I
pulled off of the drive vs what I got out of /etc/lvm/backup.  Maybe I
am just mis-reading it.  I will continue my research for a bit.




> When you do the pvcreate --uuid it won't use anything except the uuid info
> so the rest may not need to be exactly right, if you have to do a
> vgcfgrestore to get it to read the rest of the info will be used.

Oh, thank you.   I did see that things got somewhat different on the
target drive when I did "pvcreate --uuid --restorefile."  I got paranoid
when I saw that, and re-copied the ddrestore file back to the target
drive before I did anything else.   Should I do "pvcreate --uuid
--norestorefile," instead?  Then, once it is back in the machine, do the
pvscan and vgcfgrestore, and expect good things?



> I have seen some weird disk controller failures that appeared to zero out
> the first bit of the disk (enough to get the partition table, grub, and the
> pv header depending on where the first partition starts).

I APPEAR to have a partition table, containing an NTFS partition, an LVM
partiton ( the one that I am concentrating on ) and a Linux partion.  I
would have thought that it was all LVM, but my memory could easily be
wrong.



> You will need to reinstall grub if this was the bootable disk, since there
> were 384 bytes of grub in the sector with the partition table that you know
> are missing.

Fortunately, this is all data, nothing to do with the boot sequence,
except that the machine will not boot with the missing PV.



Thank you,
Brian

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