Adding an external encrypted drive with LVM to Ubuntu Linux

I recently added an external eSATA drive to my home computer so I could back up critical data from my home network to one drive. I bought a Western Digital 1TB “green” drive and a Thermaltake external hard drive enclosure with eSATA and USB connectors.

Since my internal hard drives are encrypted it didn’t make sense to back up all of that data to an unencrypted external drive. I’d read Uwe Hermann’s excellent how-to article on disk encryption, but he didn’t cover setting up an LVM partition, which I always use so I can change drive volume sizes on the fly.

This is what I did to set up an external encrypted drive with LVM on an Ubuntu system:

  1. Open a terminal
  2. Get a root prompt:
    sudo /bin/bash
  3. Watch the system log:
    tail -f /var/log/messages
  4. Attach the external drive. The system log tells me that it was detected as /dev/sdc.
  5. Check the drive for bad blocks (takes a couple of hours):
    badblocks -c 10240 -s -w -t random -v /dev/sdc
  6. Write random data to the entire drive. This step takes all night, but it ensures that never-written drive space can’t be differentiated from encrypted data if someone ever tries to crack the drive. (If you’re going to do this, you might as well do it right.)
    shred -v -n 1 /dev/sdc
  7. Create one big LVM partition on the drive using fdisk. Set up one big primary partition /dev/sdc1, set the tag to system id “8e” LVM, and write the changes to disk:
    > fdisk /dev/sdc                                                                                                                                              
    Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel                                                                                                  
    Building a new DOS disklabel with disk identifier 0xa6846916.                                                                                                                       
    Changes will remain in memory only, until you decide to write them.                                                                                                                 
    After that, of course, the previous content won't be recoverable.                                                                                                                   
    
    
    The number of cylinders for this disk is set to 121575.
    There is nothing wrong with that, but this is larger than 1024,
    and could in certain setups cause problems with:               
    1) software that runs at boot time (e.g., old versions of LILO)
    2) booting and partitioning software from other OSs                                                                                                                                 
       (e.g., DOS FDISK, OS/2 FDISK)                                                                                                                                                    
    Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)                                                                                                      
                                                                                                                                                                                        
    Command (m for help): p                                                                                                                                            
                                                                                                                                                                                        
    Disk /dev/sdc: 999.9 GB, 999989182464 bytes                                                                                                                                         
    255 heads, 63 sectors/track, 121575 cylinders                                                                                                                                       
    Units = cylinders of 16065 * 512 = 8225280 bytes                                                                                                                                    
    Disk identifier: 0xa6846916                                                                                                                                                         
                                                                                                                                                                                        
       Device Boot      Start         End      Blocks   Id  System                                                                                                                      
                                                                                                                                                                                        
    Command (m for help): n                                                                                                                                            
    Command action                                                                                                                                                                      
       e   extended                                                                                                                                                                     
       p   primary partition (1-4)                                                                                                                                                      
    p                                                                                                                                                                  
    Partition number (1-4): 1                                                                                                                                          
    First cylinder (1-121575, default 1): [ENTER]                                                                                                                      
    Using default value 1
    Last cylinder, +cylinders or +size{K,M,G} (1-121575, default 121575): [ENTER]
    Using default value 121575
    
    Command (m for help): t
    Selected partition 1
    Hex code (type L to list codes): 8e
    Changed system type of partition 1 to 8e (Linux LVM)
    
    Command (m for help): p
    
    Disk /dev/sdc: 999.9 GB, 999989182464 bytes
    255 heads, 63 sectors/track, 121575 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes
    Disk identifier: 0xa6846916
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/sdc1               1      121575   976551156   8e  Linux LVM
    
    Command (m for help): w
    The partition table has been altered!
    
    Calling ioctl() to re-read partition table.
    Syncing disks.
  8. Use cryptsetup to encrypt the drive:
    cryptsetup --verbose --verify-passphrase luksFormat /dev/sdc1
  9. Unlock the drive:
    cryptsetup luksOpen /dev/sdc1 backupexternal
  10. Create the LVM physical volume:
    pvcreate /dev/mapper/backupexternal
  11. Create the LVM volume group:
    vgcreate xbackup /dev/mapper/backupexternal
  12. Create a logical volume within the volume group:
    lvcreate -L 500G -n backupvol /dev/xbackup
  13. At this point you have a device named /dev/xbackup/backupvol, so create a filesystem on the logical volume:
    mkfs.ext4 /dev/xbackup/backupvol
  14. Mount the volume:
    mount /dev/xbackup/backupvol /mnt/backup
  15. To get the volume to mount automatically at boot time add this line to your /etc/fstab file:
    /dev/xbackup/backupvol      /mnt/backup     ext4    defaults        0 5
  16. To be prompted for the decryption key / passphrase at boot time first get the drive’s UUID:
    ls -l /dev/disk/by-uuid

    (In my example I use the UUID for /dev/sdc1)

  17. Then add this line to the /etc/crypttab file:
    backupexternal UUID=[the UUID of the drive] none luks

That’s it. You now have an external, encrypted hard drive with LVM installed. You’ve created one 500GB volume that uses half the disk, leaving 500GB free for other volumes, or for expanding the first volume.

Hope you find this useful.

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