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Minos
Asked: 2015-09-17 00:25:10 +0800 CST

LUKS encrypted device gone missing

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The 2TB disk that I use as an encrypted backup, is now reported by Ubuntu as being just free space. The encryption was setup as a LUKS encrypted device.

The output of sudo fdisk -l reports:

Disk /dev/sdc: 2000.4 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x6b6edeba

Device Boot      Start         End      Blocks   Id  System

Note that there is no partition information reported (there was only one partition on the disk).

Trying to open the disk with sudo cryptsetup luksOpen /dev/sdc crypt1 returns the error:

Device /dev/sdc is not a valid LUKS device.

Now luckily I have backups of the backup, so I can live with the data being going this time, however I need to know: What caused it and/or how I can fix it, because otherwise I can't trust my backup to be there in the future and I will have to find a different solution.

Edit1: Per request a screenshot of the Disks Utility: enter image description here

This is on Ubuntu 14.04.3 LTS.

partitioning

1 Answers

  1. Running sudo file -s /dev/sdc returns:

    /dev/sdc: x86 boot sector

    Making it very probable that the LUKS header, which was raw on disk, was overwritten by a bootloader. The default for Ubuntu without LVM seems to be to install a LUKS volume directly to the disk.

    The system is actually dual-booting Windows 10 and Ubuntu (should have mentioned this, sorry!). To find out the culprit (hint: It's always Microsoft): we parse the strings in the first sector of the disk:

    sudo dd bs=512 count=1 if=/dev/sdc 2>/dev/null | strings

    Which shows for the backup disk with the lost LUKS header:

    Invalid partition table
Error loading operating system
Missing operating system

    The default boot drive has Grub 2 and for the same command returns:

    GRUB 
Geom
Hard Disk
Read
 Error

    The Windows 10 disk with the Windows 10 boatloader:

    Invalid partition table
Error loading operating system
Missing operating system

    Bingo! Now I know that I manually installed the Windows bootloader only to the Windows 10 disk, as I had accidentally overwritten it myself with a Grub bootloader and I know the LUKS volume was still there afterwards. However, I have run several automatic Windows 10 repair utilities, as my Windows 10 install keeps freezing/crashing. So it could be possible that one of them decided to appropriate the backup disk for an extra bootloader.

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