Re: Help restoring a corrupted PV partition ( 18th )

On Mon, Oct 18, 2021 at 11:40:39PM +0200, Zdenek Kabelac wrote:
> Dne 18. 10. 21 v 20:08 Brian McCullough napsal(a):
> >
> >I have had a disk go bad on me, causing me to lose one PV.

Thank you for the thoughts, Zdenek.

No, it was a hardware failure.  Bad blocs, unreadable sectors, etc.

According to ddrescue, this partition was recovered without any
problems, although, as I observe later, the first part of the partition
is zero.



> >
> >If I am not providing sufficient, or the proper, information, feel free
> >to ask for more.
> >
> >
> >I seem to have retrieved the partition using ddrescue and put it on to
> >a new drive, but it seems to be missing some label information, because
> >pvscan doesn't recognize it as a PV partition.
> >
> >Using hexdump, I see the string " LVM2 " at 0x1004, but nothing before
> >that.  The whole 16 bytes is:
> >
> >0x01000  16 d6 8e db 20 4c 56 4d  32 20 78 5b 35 41 25 72
> >                         L  V  M  2
> >
> >
> >
> >I find what appears to be an LVM2 vgconfig block starting at 0x01200,
> >extracted that to a file and was able to read the UUID that this PV
> >should have.  It is one of about a dozen that make up this VG.
> >
> >
> >On another machine, I dumped a PV partition, and find "LABLEONE" at
> >0x200, with the same " LVM2 " at 0x01000.
> >
> >I was concerned that my dump was offset, but the comparison to the
> >"good" one suggests that that isn't the problem, but just the missing
> >"LABLEONE" and related information at 0x0200.
> >
> >
> >How to fix?
> >
> >If I do a "pvcreate --uuid xxxx" would this fix that recovered partition
> >so that pvscan and friends can work properly, and I can finally boot
> >that machine?
> 
> Hi
> 
> It's quite important to be aware how the disk corruption happened.
> Was this plain disk hw error -  or some crash of raid setup ?
> 
> Normally you could restore PV with this:
> 
> pvcreate --uuid  XXXX --restorefile  file_with_vg_backup  /dev/ddddd
> vgcfgrestore --restorefile   file_with_vg_backup   vgname
> 
> 
> But if the content of device was scramble by some 'raid' bug - you might
> have problem to retrieve any usable data afterward.
> 
> 
> Regards
> 
> Zdenek
> 

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