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Re: [linux-lvm] LVM pretends it has more space than it actually has



I managed to get all my data back by deleting the LVM volumes and recreating it without formatting the drives. I did have to run fsck on my data volume, but all data was intact as far as I could see.

And I also think I know what went wrong. Pretty much every reboot my raid-1 (for /boot) and my raid-5 MD-devices switch places with each other. So sometimes it's /dev/md126, the other times it's /dev/md127. I must have used the wrong device after a reboot, mistakenly thinking it was the LVM or boot partition.

On 21-9-2011 20:32, Gijs wrote:
Unfortunately I can't find all the old LVM configs that the system used. I was in the process of moving my root filesystem to the raid-5 array. Since I needed the root to be unmounted for that, I used a FC15 USB-bootable rescue system to do the copying of the root to the raid-5 array. And that's when things went wrong. Since the rescue system is pretty much run from memory, I don't have the LVM configs that were created when I was using the rescue system. I do have older configs that were created when I was creating the raid-5 array on the system itself, but those don't show anything wrong from what I can see. (and I guess that's correct, since nothing was wrong at that time)

I tried assembling/recreating an array on the PV-device, but that just gave me the error "mdadm: no raid-devices specified." So I can't really find an array on the LVM devices either.

Some info I got from the PV:
[root poseidon ~]# pvdisplay -m /dev/md127
  --- Physical volume ---
  PV Name               /dev/md127
  VG Name               raid-5
  PV Size               3.64 TiB / not usable 0
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              952919
  Free PE               5252
  Allocated PE          947667
  PV UUID               ZmJtA4-cZBL-kuXT-53Ie-7o1C-7oro-uw5GB6

  --- Physical Segments ---
  Physical extent 0 to 714687:
    Logical volume      /dev/raid-5/data
    Logical extents     0 to 714687
  Physical extent 714688 to 714933:
    FREE
  Physical extent 714934 to 714953:
    Logical volume      /dev/raid-5/data
    Logical extents     947647 to 947666
  Physical extent 714954 to 719959:
    FREE
  Physical extent 719960 to 952918:
    Logical volume      /dev/raid-5/data
    Logical extents     714688 to 947646

The empty spaces inbetween are from LVs there were created before. And the 3rd segment is from when I tried to resize the data-LV to see if that made any difference. It obviously didn't since it was the PV that was actually too small, not the LV, which I figured out later.

From what you say, it indeed sounds like I messed up some command that caused an array to be created on an LV, but I can't really find any evidence that I really did that. Is there any other explanation that LVM is acting this way? Is it perhaps possible to tell LVM to run of the configuration stored in /etc/lvm, instead of the metadata embedded on the PV?

There's also something that I don't understand. Why is it just the data-LV? I had a swap and root LV as well, and those activated just fine. Why would LVM have trouble activating the data-LV when it had no trouble activating the swap/root-LV?

On 19-9-2011 22:41, Ray Morris wrote:
First, if at all possible make a copy of the underlying block
device using dd or dd_rescue. Very often the most severe damage
is done during the attempt at recovery.

Then let's find the oldest back up copies on the LVM meta data to
see if we can verify how things were set up when they were working.
This will find metadata over 50 days old:

find /etc/lvm/archive -mtime +50

mainly what we're looking for is to see if any mdadm RAID devices
were used as PVs at some point.

Next try mdadm --assemble --readonly --assume-clean /dev/sdFOO to see
if you can assemble an array using the lower level device (which is
also marked as a PV right now). If it assembles, do:
pvdisplay -m /dev/md0
to see if it's a PV, and check to see if it has a filesystem.

Based on the messages you got, it looks like /dev/md0 at one point
was the PV, rather than being assembled from LVs.

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