Resizing LVM-on-LUKS

This article follows the process of resizing and shrinking an LVM-on-LUKS-on-GPT partition, such that an extra (plain) partition can be added in the unused space cleared up on the end of the hard drive. You can also use GParted GUI tool to resize LUKS partition, which may be easier and quicker for beginners.

Method

We do all the resizes from the innermost partition to the outermost on, keeping 1G buffers along the way on each step. It is possible to keep smaller buffers, but that should be done carefully, especially where there are manual calculations.

The filesystem we work on will have the following strucure:

# lsblk

NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                   8:0    0 111.8G  0 disk
├─sda1                8:1    0    99M  0 part  /boot
└─sda2                8:2    0 111.7G  0 part
  └─vgroup          254:0    0 111.7G  0 crypt
    ├─vgroup-lvroot 254:1    0    30G  0 lvm   /
    └─vgroup-lvhome 254:2    0  81.7G  0 lvm   /home

The goal is to clear up unused space and create a new partition, sda3, without any data loss. All filesystems are assumed to be ext4.

The entire process should run from a live USB Arch system to avoid any filesystem corruption.

Process

Warning: Do not run any of this code by copy-pasting, you need to adapt all these commands to your specific setup.

Note: It is highly recommended to check your work after each step by checking the filesystem, LVM, and/or LUKS volume integrity.

Note: It is highly recommended to write out the exact transition plan so that at each step you know exactly which partition size you are going to need.

Shrink LVM-on-LUKS

Boot and setup

Boot into your live USB flash installation media.

Decrypt the LUKS volume:

# cryptsetup luksOpen /dev/sda2 cryptdisk

Resize filesystem and LVM logical volume

Follow these instructions.

You can run a fsck just to make sure nothing broke:

# e2fsck -f /dev/vgroup/lvhome

Resize LVM physical Volume

To calculate the new LVM physical volume size, use a simple formula: NEW_VOLUME_BYTES = PE_SIZE * PE_COUNT + UNUSABLE_SIZE:

pvdisplay /dev/mapper/cryptdisk

...
PV Size               950.05 GiB / not usable 4.00 MiB
...
PE Size               4.00 MiB
...
Allocated PE          116303
...

Using the formula above: (116303 * 4 MiB + 4 MiB) in Bytes = 487814332416.

Resize the volume. This command is safe since it will exit early if the new size would not fit all the existing extents:

# pvresize --setphysicalvolumesize 487814332416B /dev/mapper/cryptdisk

Resize LUKS volume

To calculate the new LUKS volume size, use a simple formula:

(116303 extents + 1 unusable extent) * 4194304 B/extent / 512 B/sector = 952762368 sectors

Resize the LUKS volume:

# cryptsetup -b $NEW_LUKS_SECTOR_COUNT resize cryptdisk

Resize the partition

To calculate the new partition size, use a simple formula: . The - 1 is because parted takes an inclusive sector end parameter.

Close the LUKS volume to resize offline. You will probably need to deactivate LVM volumes on the cryptdisk or it will not close.

# vgchange -a n vgroup
# cryptsetup close cryptdisk

Use to resize the partition:

# parted /dev/sda
 (parted) unit
 Unit?  [compact]? s
 (parted) p
 ...
  2      8003584s  2000408575s  1992404992s

Using the formula above returns:

(parted) resizepart 2 960770047
 Warning: Shrinking a partition can cause data loss, are you sure you want to continue?
 Yes/No? y
 (parted) q

At this point you can reopen the LUKS volume and remount partitions. You will need to manually reactive the LVM partitions since if you manually deactivated them above.

# cryptsetup luksOpen /dev/sda2 cryptdisk
# vgchange -a y vgroup

Enlarge LVM on LUKS

Enlarging a LVM-on-LUKS logical partition, for instance after migrating to a larger hard disk, is done in the opposite way - from the outermost to the innermost partition:

primary partition(LUKS device{volume group[(logical partition1)(logical partition2-->)]})

Preparation

Create a new partition on the new hard disk of wanted size, f.i. by using GNU Parted, and clone the old partition , containing your LUKS container, into the new partition :

# dd if=/dev/sdX1 of=/dev/sdY1 bs=4M

Extending the physical segments of the cryptdevice

Now, open the cryptdevice CryptDisk on the new hard disk:

# cryptsetup open /dev/sdY1 CryptDisk

Take a look at your current physical volume. In this example, we have a cryptdevice CryptDisk containing a volume group of two partitions and :

By taking the total physical extents (PE) times the PE's size, we get the total size of the physical volume (PV), in this case 118.75 GiB. Although pvdisplay does not show the free extents, we can enlarge the PV to use all the available remaining space of the partition:

# pvresize /dev/mapper/CryptDisk

Now we get:

# pvdisplay -m

...
 --- Physical Segments ---
 Physical extent 0 to 6399:
   Logical volume      /dev/CryptVolumeGroup/root
   Logical extents     0 to 6399
 Physical extent 6400 to 30398:
   Logical volume      /dev/CryptVolumeGroup/home
   Logical extents     0 to 23998
 Physical extent 30399 to 60922:
   FREE

Note the free extents at the end of the PV. Calculate the size difference by taking the free physical extends times PE size - in that case (60922-30399)*4 MiB = 119.2 GiB.

Resizing the logical volume

Now we are going to resize the second logical volume (LV), in this case containing the /home partition, by the size of the free physical extents minus some safety space:

# lvresize -L +119G /dev/CryptVolumeGroup/home

Note the new size of the second logical volume. Calculate its total size by taking the total logical extends time the PE size - in that case 53438 * 4 MiB = 208.7 GiB:

Resizing the encrypted volume

Now we are going to resize the encrypted volume itself. By taking in account the total size of the logical volume minus some safety space:

# resize2fs -p /dev/CryptVolumeGroup/Home 208G

Execute e2fsck, if asked. That's it.