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My vgdisplay shows 0 PE's. But if i mount the volume and run df -h i get loads of free space. Is this something to do with the way lvm allocates extents? I don't get similar behaviour from my other vg. Find below the vgdisplay output and df output.

--- Volume group ---
  VG Name               lvm-root
  System ID             
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                1
  Open LV               1
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               56.80 GiB
  PE Size               4.00 MiB
  Total PE              14542
  Alloc PE / Size       14542 / 56.80 GiB
  Free  PE / Size       0 / 0   
  VG UUID               C4S16g-JcUU-NsN3-yR0H-nscI-9SYh-LJzmG5

And the df output:

 df -h /mnt/
    Filesystem            Size  Used Avail Use% Mounted on
                           56G   13G   41G  25% /mnt

P.S: This is a root / (ext3) filesystem on my laptop. and currently there is a grub failure, am working my way out of.

[EDIT]: I managed to boot into a live ubuntu usb disk and now am trying to mount the filesystem. But i get Buffer I/O error. Unable to read superblock. Running e2fsck, gives me 1.41.12 (17-May-2010)

e2fsck: Attempt to read block from filesystem resulted in short read while trying to open /dev/mapper/lvm--root-lvol0
Could this be a zero-length partition?

And oh, i tried to find the superblock using dumpe2fs i get this:

root@ubuntu:~# dumpe2fs /dev/mapper/lvm--root-lvol0 
dumpe2fs 1.41.12 (17-May-2010)
dumpe2fs: Attempt to read block from filesystem resulted in short read while trying to open /dev/mapper/lvm--root-lvol0
Couldn't find valid filesystem superblock.

Any hopes of recovering data?

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Is your question about LVM, or is it about FS recovery? – Ignacio Vazquez-Abrams Jul 13 '11 at 6:25
Free PE extents are different from free space on one of your logical volumes: the first are free space in the volume group which can be used to create new/larger logical volumes, while 'df' reports on free space on the filesystem within a logical volume. – eldering Jul 13 '11 at 8:20
@eldering: Thanks for the clarification. @Ignacio: I guess it was more an attempt to solve that strange behaviour. To be fair, a reboot an grub-reinstall has solved the problem. I am guessing the usb hd had failed previously causing the problem. Thanks for the help. – Software Mechanic Jul 14 '11 at 17:28

Turned out the problem was a usb port connection failure. Those were partitions from a usb hard disk. Will close the question with this answer.

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