[TriLUG] Help with a "broken" LVM drive

[David Both via TriLUG]

You may not have a PV if the storage device was partitioned. Have you run vgs, 
pvs, and lvs, which all search for LVM entities? There is also pvdisplay, 
lvdisplay and vgdisplay, as well as pvscan, vgscan, and lvscan. Also, vgmknodes 
can create new device nodes for all existing volume groups.

Good luck.

-- 


*********************************************************
David P. Both, RHCE
He/Him/His
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www.both.org - My personal web site
www.Linux-Databook.info - Home of the DataBook for Linux
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not in its price.

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On Wed, 20 Oct 2021, Brian McCullough via TriLUG wrote:

> Date: Wed, 20 Oct 2021 15:40:06
> From: Brian McCullough via TriLUG <trilug at trilug.org>
> Reply-To: Brian McCullough <bdmc at bdmcc-us.com>,
>     Triangle Linux Users Group General Discussion <trilug at trilug.org>
> To: Triangle Linux Users Group discussion list <trilug at trilug.org>
> Subject: [TriLUG] Help with a "broken" LVM drive
> 
>
> Folks,
>
> The more that I work on this, the more that I feel that paranoia is the
> better part of valour.
>
>
> I recently ( a week ago or so ) had a drive go bad on me, bad blocks,
> unreadable sectors, the works.
>
> Because of that, the machine will not boot, and stops during that
> process and asks for the root password.
>
> I removed the drive, bought a "work" drive and started with ddrescue.
>
> According to fdisk, there are three partitions on this drive: a Windows
> partition of more than half the size ( which is a bit strange, since it
> would have had no use in one of my machines ), a 300GB LVM partition,
> and a Linux partition of about 30G.  OK, it has been so long since I
> first set up this drive that I have to accept this, I guess.  It is a
> 3TB portable Seagate, so I can accept that it was initially
> pre-formatted as Windows.
>
>
> Using ddrescue, I was apparently able to recover both the LVM and Linux
> partitions ( separately ).
>
> When I ran ddrescue on the LVM partition, it ran for some hours and then
> completed, recording zero errors.
>
>
> I found some data at the beginning for the LVM partition that indicated
> that it had been an LVM partition.  I found the string " LVM2 " at just
> after 0x01000, and something that looks a lot like a ( partial )
> vgconfig file at 0x01200, even if that seems to start part-way into that
> file.
>
> I don't find any evidence of LVM on either of the other two partions.
>
> I did not find the "LABELONE" tag which should be at the beginning of a
> PV, just zeros.  ( possibly part of the ddrescue process??? )
>
> OK, that's the preamble.  ( Sorry )
>
> Since I am able to start to boot the machine, I was able to get to
> /etc/lvm/backup and retrieve the appropriate vgconfig file that this
> partition should be part of.  In the data on the partition itself, I
> found what should probably be the UUID for this PV.  What bothers me is
> that I do not find that UUID in the current vgconfig backup file. (
> Well, one of the things that bothers me. )  That UUID does show up in
> archive versions of that file.  However, if that UUID is no longer used,
> why does the machine not boot?  Oh, well.
>
> I also purchased a drive to replace that partition, and used ddrescue to
> copy the contents to it.   However, at the moment, the partition is not
> recognized as a PV.
>
> If I use the UUID that I found on that partition and run "pvcreate
> --uuid" should I use "--restorefile" or "--norestorefile"?  I tried this
> with --restorefile, using the data that I dd'd from the partition, which
> turned out to be an incomplete vgconfig file, and it overwrote what was
> on the partition at 0x01200, so I stopped at that point.  However, now
> that I have been examining things, including the vgconfig backup file
> from the machine, that have been properly successful if I was using the
> proper vgconfig file.
>
>
>
> Now that I have talked through all of that, I am wondering whether I am
> possibly heading down the correct path, and have some hope of restoring
> this machine to operation?
>
> Do you have any further suggestions for tests or things that I should be
> doing, or whether I should just go ahead with pvcreate?  If I run
> pvcreate on a different machine ( where I am doing all of my recovery
> work ), I suspect that I should not run vgcfgrestore until I re-attach
> the new drive to the original machine, correct?
>
> ( The instructions that I have been reading say to run pvcreate followed
> by vgcfgrestore. )
>
>
>
>
> If there anything more that I can say, answer questions or perform any
> more experiments, just say so.
>
>
> Thank you,
> Brian
>
>