Resizing raid5 with mdadm, lvm and luks for encryption on debian wheezy

This guide will show you how to setup a simple mdadm, lvm test environment in which you can experiment with changes you want to execute on a real disk system.

Setup the test environment

You can of course use your own disks. In my case i did a trial run of the needed steps by using losetup to map a data file to a loop device.

  dd if=/dev/zero of=diska bs=1M count=300
  dd if=/dev/zero of=diskb bs=1M count=300
  dd if=/dev/zero of=diskc bs=1M count=300
  dd if=/dev/zero of=diskd bs=1M count=300
  losetup /dev/loop0 diska
  losetup /dev/loop1 diskb
  losetup /dev/loop2 diskc
  losetup /dev/loop3 diskd

  # Create raid 5 with one disk missing
  mdadm -Cv /dev/md2 -l5 -n3 /dev/loop0 /dev/loop1 missing

  # Add luks cryptolayer ontop
  cryptsetup luksFormat /dev/md2
  cryptsetup luksOpen /dev/md2 cryptotest

  # Add lvm structure
  pvcreate /dev/mapper/cryptotest
  vgcreate testvg /dev/mapper/cryptotest
  lvcreate -l 100%FREE -n testlv testvg

  # Create filesystem
  mkfs.ext3  /dev/mapper/testvg-testlv
  mount /dev/mapper/testvg-testlv test/

You can now copy your data onto the raid 5 and when done add the missing disk to the final raid. You can of course use three disks from the start.

Add missing disk to the raid 5

  # Add missing device
  mdadm --add /dev/md2 /dev/loop2

Growing the raid 5 by adding a forth disk

Once your data has been copied you may want to add the now free disk to the raid of md2.

  # Add disk and resize md2
  mdadm --add /dev/md2 /dev/loop3
  mdadm --grow --raid-devices=4 /dev/md2

  # Check the sync process and the final result
  cat /proc/mdstat
  mdadm --detail /dev/md2
  umount /tmp/test/test

  # Resize the crypt layer and check the result
  cryptsetup resize cryptotest
  fdisk -l /dev/mapper/cryptotest

  # Resize physical volume and check the result
  pvresize /dev/mapper/cryptotest
  pvdisplay

  # Resize logical volume and check result
  lvextend -l +100%FREE /dev/mapper/testvg-testlv
  lvdisplay

  # Resize filesystem
  e2fsck -f /dev/mapper/testvg-testlv
  resize2fs /dev/mapper/testvg-testlv
  mount /dev/mapper/testvg-testlv test

Cleanup of the test environment

Of course you should not do these steps on the real raid. These steps are just needed when you want to cleanup your testenvironment.

  umount /tmp/test/test
  lvremove testvg testlv
  vgremove testvg
  pvremove  /dev/mapper/cryptotest
  cryptsetup close /dev/mapper/cryptotest
  mdadm --manage /dev/md2 --stop
  losetup -d /dev/loop0
  losetup -d /dev/loop1
  losetup -d /dev/loop2
  losetup -d /dev/loop3