Resizing a root LVM volume

Resize a VM’s root LVM volume if you find it too small

All of the VMs created in this guide are based in a VM template that has a 10 GiB bootdisk. What if you need a VM that needs more space for its root filesystem?

You can resize a VM’s bootdisk through the Proxmox VE web console, then extend the root LVM filesystem inside of it over the new space. The procedure is not hard but, since it manipulates the root LVM filesystem while it is active, you must be careful when going through it.

As an example, this appendix will show you how to give 5 GiB more to the root filesystem of the UrBackup server.

Important

Do a backup of the VM where you will resize the root filesystem
The procedure explained here has a non-trivial amount of danger for the root filesystem involved.

Play it safe and make a backup of the VM before you start resizing its bootdisk.

Resizing the storage drive on Proxmox VE

You can expand any hard disk attached to a VM easily on Proxmox VE:

Get into your Proxmox VE server’s web console and select the VM, then shut it down:
bkpserver VM shown stopped in its summary view
In this example, the VM to stop is bkpserver. Ensure it is stopped by checking both its activity icon on the sidetree and in its Summary view as highlighted above.
With the VM stopped, get into its Hardware tab, select the hard disk containing the VM’s root filesystem (this is the bootdisk for Proxmox VE) and then press on Resize disk:
Disk actions menu enabled for chosen bkpserver hard disk scsi0
The hard disk containing the root filesystem of the bkpserver VM is the one identified as the scsi0 unit for Proxmox VE and has 10 GiB of capacity.
After clicking on the Resize option of the Disk Action menu, the next form will appear:
Resize disk form
The Disk field identifies the hard disk you are about to resize which, in this case, is the bkpserver’s scsi0 unit. The Size Increment (GiB) field is where you indicate by how many gibibytes you want to increase the size of this particular hard disk.
Important
Proxmox VE’s web console only supports INCREASING hard disks sizes, not reducing them.
Type the size increment, in gibibytes, to apply to the hard disk and click on Resize Disk:
Resize disk form set with 5 GiB increment for bkpserver hard disk scsi0
In this example, the bkpserver’s scsi0 unit will be made 5 GiB bigger.
Proxmox VE will apply the resize almost immediately after showing you a quick progress window that will close itself. Then, you will be able to see the new size shown in the hard disk description:
bkpserver hard disk scsi0 resized
The bkpserver’s scsi0 hard disk unit now has a total of 15 GiB, from an initial capacity of 10 GiB.

Extending the root LVM filesystem on a live VM

The hard disk is bigger now, but the VM’s root filesystem is not using that extra space yet. You need to extend it over the newly available storage. Continuing with the example, here you will see how to extend the root filesystem of the bkpserver VM while it is running. Therefore, start the VM and proceed with the remainder of this procedure:

bkpserver VM shown running in its summary view

By the way, notice in the Summary view of the VM how the Bootdisk size also reflects the new size of the hard disk scsi0.

Warning

Applying this procedure is dangerous!
The following procedure could make your VM’s filesystem (and the VM itself) unusable if you are not careful!

If you have not done a backup of the VM yet, this is the moment to do so.

Resizing the related partitions

Before you can extend the root LVM volume, you need to resize the partition in which it is found:

Open a remote shell into the VM with mgrsys user, then check with fdisk if the system truly sees the full size of the disk:

$ sudo fdisk -l
Disk /dev/sda: 15 GiB, 16106127360 bytes, 31457280 sectors
Disk model: QEMU HARDDISK
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x5dc9a39f

Device     Boot   Start      End  Sectors  Size Id Type
/dev/sda1  *       2048  1556479  1554432  759M 83 Linux
/dev/sda2       1558526 20969471 19410946  9.3G  f W95 Ext'd (LBA)
/dev/sda5       1558528 20969471 19410944  9.3G 8e Linux LVM


Disk /dev/sdb: 250 GiB, 268435456000 bytes, 524288000 sectors
Disk model: QEMU HARDDISK
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 /dev/mapper/bkpserver--vg-root: 8.69 GiB, 9328132096 bytes, 18219008 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 /dev/mapper/bkpserver--vg-swap_1: 544 MiB, 570425344 bytes, 1114112 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

Notice the Disk /dev/sda line, it says that the sda hard disk has the expected 15 GiB. Also see how inside sda there are three partitions: sda1, sda2 and sda5. The sda5 partition is the one you want to spread over the extra storage space available, since it is the one that contains the root LVM volume (and also the swap volume). But this sda5 partition is inside the W95 Ext'd (LBA) sda2 one, so you need to expand first the sda2 partition to the end of the sda drive.

Now you’re going to install another partition tool that will help you resize the sda2 and sda5 partitions easily. The tool is parted:
```
$ sudo apt install -y parted
```

Launch parted over the /dev/sda drive:

$ sudo parted /dev/sda

You will get in the parted shell:

GNU Parted 3.6
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted)

Execute print to check how parted sees the sda partitions:

(parted) print
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 16.1GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
1      1049kB  797MB   796MB   primary   ext4         boot
2      798MB   10.7GB  9938MB  extended               lba
5      798MB   10.7GB  9938MB  logical                lvm

Notice that the Number is what identifies each partition: the sda2 is shown just as number 2, and sda5 as 5.

Resize the partition 2 with the following resize command:

Warning

Using parted on a live root filesystem is dangerous!
The parted program applies the changes in the partition table immediately, unlike fdisk that works first on a temporal table on memory.

(parted) resizepart 2 -1s

It will not return any output. Check with print that parted has resized the partition 2:

(parted) print
Model: QEMU QEMU HARDDISK (scsi)
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 16.1GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
1      1049kB  797MB   796MB   primary   ext4         boot
2      798MB   16.1GB  15.3GB  extended               lba
5      798MB   10.7GB  9938MB  logical                lvm

Now, apply the resizing to partition 5:

(parted) resizepart 5 -1s

Again, use print to verify the resizing of the partition 5:

(parted) print
Model: QEMU QEMU HARDDISK (scsi)
Disk /dev/sda: 16.1GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type      File system  Flags
1      1049kB  797MB   796MB   primary   ext4         boot
2      798MB   16.1GB  15.3GB  extended               lba
5      798MB   16.1GB  15.3GB  logical                lvm

Type quit or just use Ctrl+C to exit parted:
```
(parted) quit
Information: You may need to update /etc/fstab.
```
Notice that, when exiting, parted will warn you about updating the /etc/fstab file. In this case it will not be necessary.

Extending the `root` LVM volume

With the real partitions updated, now you can extend the root LVM filesystem in the newly available space:

First you must extend the physical volume that corresponds to the sda5 partition. Check with pvs its current state:
```
$ sudo pvs
  PV         VG           Fmt  Attr PSize PFree
  /dev/sda5  bkpserver-vg lvm2 a--  9.25g 36.00m
```
Notice that its PSize is 9.25 GiB.

Use pvresize to expand the sda5 PV:

$ sudo pvresize /dev/sda5
  Physical volume "/dev/sda5" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized

Then verify with pvs that the resizing has been done:

$ sudo pvs
  PV         VG           Fmt  Attr PSize  PFree
  /dev/sda5  bkpserver-vg lvm2 a--  14.25g <5.04g

Above you can see that PSize is now 14.25 GiB, from which 5.04 GiB are free (PFree column).

Now you can resize the root LV itself. First, check its current status:

$ sudo lvs
  LV     VG           Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   bkpserver-vg -wi-ao----  <8.69g
  swap_1 bkpserver-vg -wi-ao---- 544.00m

Its LSize is 8.69 GiB and, below it, you can see the swap volume (swap_1) taking up about 544 MiB.

Use the following lvextend command to extend the root volume over all the available free space in the sda5 PV:

$ sudo lvextend -r -l +100%FREE bkpserver-vg/root
  File system ext4 found on bkpserver-vg/root mounted at /.
  Size of logical volume bkpserver-vg/root changed from <8.69 GiB (2224 extents) to 13.72 GiB (3513 extents).
  Extending file system ext4 to 13.72 GiB (14734589952 bytes) on bkpserver-vg/root...
resize2fs /dev/bkpserver-vg/root
resize2fs 1.47.2 (1-Jan-2025)
Filesystem at /dev/bkpserver-vg/root is mounted on /; on-line resizing required
old_desc_blocks = 2, new_desc_blocks = 2
The filesystem on /dev/bkpserver-vg/root is now 3597312 (4k) blocks long.

resize2fs done
  Extended file system ext4 on bkpserver-vg/root.
  Logical volume bkpserver-vg/root successfully resized.

The command not only has resized the LV, but also has resized the ext4 filesystem inside (the -r option called the resize2fs command). Check again with lvs the new status of the root LV:

$ sudo lvs
  LV     VG           Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   bkpserver-vg -wi-ao----  13.72g
  swap_1 bkpserver-vg -wi-ao---- 544.00m

Now its LSize is 13.72 GiB, and the swap volume has been unaffected by the whole procedure.

As a final test, reboot the VM to verify that the changes have not messed up with the system in a bad way. This is something you may detect in the VM’s boot sequence, although you can see a VM’s boot sequence only through a noVNC shell, never through an ssh connection:
```
$ sudo reboot
```

Final note

You can apply this procedure to extend any non-root LVM filesystems kept in a Proxmox VE hard disk.

References

About resizing LVM storage

Handling VM or VM template volumes K3s cluster with two or more server nodes