Expanding the hard drive (LVM) of a Linux virtual machine

calendar October 23, 2021 nav_categories Tech nav_categories Hardware nav_tags linux nav_tags kvm nav_tags virsh nav_tags qemu nav_tags lvextend nav_tags pvresize nav_tags growpart nav_tags lsblk

I was doing some testing of using a Samba share for OSX's Time Machine backup, and needed to verify that it would actually work.

My initial test simply made sure that the Samba share showed up as an option in the Time Machine preferences, but I needed to run a Time Machine backup.

However, the Ubuntu VM I've been using for NAS migration testing only had a 25Gb disk defined, which wasn't going to be enough to run through an entire Time Machine backup.

I needed to increase the size of the disk of the Ubuntu VM, so it could accept a Time Machine backup, which is currently just south of 500Gb.

Make sure the VM is off

virsh list --all
 Id   Name                        State
--------------------------------------------
 -    ubuntu20.04-nas-testing    shut off

If it is still in the running state, shut it off:

virsh shutdown ubuntu20.04-nas-testing
Domain ubuntu20.04-nas-testing is being shutdown

Dump the current disks configuration

virsh domblklist ubuntu20.04-nas-testing
 Target   Source
-------------------------------------------------------
 vda      /kvm/images/ubuntu20.04-clone-1.qcow2

Delete any snapshots

The qemu-img command can't resize an image if that image has snapshots, so we'll need to delete any snapshots before resizing.

virsh snapshot-list ubuntu20.04-nas-testing
Name        Creation Time               State
--------------------------------------------------
 snapshot1   2021-09-01 11:31:51 -0600   shutoff

virsh snapshot-delete --domain ubuntu20.04-nas-testing --snapshotname snapshot1
Domain snapshot snapshot1 deleted

Resize the image

As, at least in my KVM system, the /kvm/images/ are all owned by root, need to use sudo to resize the image.

sudo qemu-img resize /kvm/images/ubuntu20.04-clone-1.qcow2 +500G
Image resized.

It doesn't actually perform the resize, it only configures it to use the additional space, so the Image resized. comes back almost immediately.

Verify new disk size

sudo qemu-img info /kvm/images/ubuntu20.04-clone-1.qcow2
image: /kvm/images/ubuntu20.04-clone-1.qcow2
file format: qcow2
virtual size: 525 GiB (563714457600 bytes)
disk size: 12.9 GiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: true
    refcount bits: 16
    corrupt: false

Boot the VM and extend the disk

From the KVM perspective, the disk has been resized, but we need to tell the OS (Ubuntu in this case) to resize the disk too.

  1. Verify Ubuntu sees the increased disk size:

    lsblk
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0                       7:0    0 70.3M  1 loop /snap/lxd/21029
loop1                       7:1    0 55.5M  1 loop /snap/core18/2074
loop2                       7:2    0 55.4M  1 loop /snap/core18/2128
loop3                       7:3    0 32.3M  1 loop /snap/snapd/12883
loop4                       7:4    0 67.6M  1 loop /snap/lxd/20326
loop5                       7:5    0 32.3M  1 loop /snap/snapd/12704
vda                       252:0    0  525G  0 disk
├─vda1                    252:1    0    1M  0 part
├─vda2                    252:2    0    1G  0 part /boot
└─vda3                    252:3    0   24G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0   20G  0 lvm  /

  2. Install, then use growpart to extend the partition

    sudo apt-get install cloud-guest-utils

    sudo growpart /dev/vda 3
CHANGED: partition=3 start=2101248 old: size=50325504 end=52426752 new: size=1098903519 end=1101004767

  3. Verify the partition size change

    lsblk
NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0                       7:0    0 70.3M  1 loop /snap/lxd/21029
loop1                       7:1    0 55.5M  1 loop /snap/core18/2074
loop2                       7:2    0 55.4M  1 loop /snap/core18/2128
loop3                       7:3    0 32.3M  1 loop /snap/snapd/12883
loop4                       7:4    0 67.6M  1 loop /snap/lxd/20326
loop5                       7:5    0 32.3M  1 loop /snap/snapd/12704
vda                       252:0    0  525G  0 disk
├─vda1                    252:1    0    1M  0 part
├─vda2                    252:2    0    1G  0 part /boot
└─vda3                    252:3    0  524G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0   20G  0 lvm  /

  4. Use pvresize to resize the PV (LVM Physical Volume) to use all available space

    sudo pvresize /dev/vda3
  Physical volume "/dev/vda3" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized

  5. Determine the LVM Logical Volume (LV) to extend

    df -hT | grep mapper
/dev/mapper/ubuntu--vg-ubuntu--lv ext4       20G   12G  6.6G  65% /

  6. Use the lvextend to extend (resize) the file system on the LV (LVM Logical Volume)

    sudo lvextend -r -l +100%FREE /dev/mapper/ubuntu--vg-ubuntu--lv
  Size of logical volume ubuntu-vg/ubuntu-lv changed from 20.00 GiB (5120 extents) to <524.00 GiB (134143 extents).
  Logical volume ubuntu-vg/ubuntu-lv successfully resized.
resize2fs 1.45.5 (07-Jan-2020)
Filesystem at /dev/mapper/ubuntu--vg-ubuntu--lv is mounted on /; on-line resizing required
old_desc_blocks = 3, new_desc_blocks = 66
The filesystem on /dev/mapper/ubuntu--vg-ubuntu--lv is now 137362432 (4k) blocks long.

  7. Verify resize

    df -hT  | grep mapper
/dev/mapper/ubuntu--vg-ubuntu--lv ext4      516G   12G  483G   3% /

References

How To extend/increase KVM Virtual Machine (VM) disk size https://computingforgeeks.com/how-to-extend-increase-kvm-virtual-machine-disk-size/