Mount LVM encrypted partition on external HDD - Device /dev/sdc5 is not a valid LUKS device

Question

Recently, my Ubuntu server was unable to boot on my 500Go HDD

I removed the HDD from my server case, put it in an external case, and connected it via USB to an Ubuntu laptop.

I have SSH access on this Ubuntu laptop. I can see the boot partition of the server HDD here :

poste3@poste3:/media$ df -h
/dev/sdc1                       228M   27M  189M  13% /media/poste3/695e74fd-83bb-4489-bf3b-51d256885fc9

I can list the content of this partition :

poste3@poste3:/media/poste3/695e74fd-83bb-4489-bf3b-51d256885fc9$ ls
abi-3.2.0-38-generic         memtest86+.bin
config-3.2.0-38-generic      memtest86+_multiboot.bin
grub                         System.map-3.2.0-38-generic
initrd.img-3.2.0-38-generic  vmlinuz-3.2.0-38-generic
lost+found

So it means that the disk is still readable, even with some defected sectors.

When I installed Ubuntu Server on this HDD, I remember I choose Use entire disk and set up encrypted LVM.

root@poste3:/home/poste3# fdisk -l /dev/sdc

Disk /dev/sdc: 500.1 GB, 500106779648 bytes
255 têtes, 63 secteurs/piste, 60801 cylindres, total 976771054 secteurs
Unités = secteurs de 1 * 512 = 512 octets
Taille de secteur (logique / physique) : 512 octets / 512 octets
taille d'E/S (minimale / optimale) : 512 octets / 512 octets
Identifiant de disque : 0x000d3d72

Périphérique Amorce  Début        Fin      Blocs     Id  Système
/dev/sdc1   *        2048      499711      248832   83  Linux
/dev/sdc2          501758   976769023   488133633    5  Étendue
/dev/sdc5          501760   976769023   488133632   8e  LVM Linux

so I did the following :

sudo apt-get install lvm2 cryptsetup
sudo modprobe dm-crypt
cryptsetup luksOpen /dev/sdc5 crypt
Device /dev/sdc5 is not a valid LUKS device.

Can you help me to mount this partition ? I don't understand why it fails...is it because physical defects in the disk ? Thanks

Solution

First, check if the partition is really encrypted :

#cryptsetup -v luksDump /dev/sdc5
#Command failed with code 22: Device /dev/sdc5 is not a valid LUKS device.

oups, this volume wasn't actually encrypted :( so then

 #lvscan
 inactive          '/dev/serveur/root' [464,48 GiB] inherit
 inactive          '/dev/serveur/swap_1' [1012,00 MiB] inherit

so we need to activate it:

#modprobe dm-mod
#vgchange -ay

and then simply mount the partition :

#mount /dev/serveur/root /media/rescue/

I thought my HDD was defected, and LVM volume encrypted, but it wasn't the case. So next time I'll think more simple, and I'll try the basics first.