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Increase diskstorage for Linux VMs

The overall process involves several layers: disk → partition → LVM physical volume → LVM logical volume → filesystem. Each layer has its own size and doesn't grow automatically just because the layer below it got bigger — that's why several steps are needed.

Before you start: Although these steps are generally safe and non-destructive, it's recommended to create a backup or snapshot of the VM beforehand, especially in production environments.

1. Check the new disk size

fdisk -l

Lists all block devices and their partitions. Check whether the disk (e.g. /dev/sda) already shows the larger total size. If not, reboot the VM once so the kernel picks up the new disk size.

2. Resize the partition

cfdisk

In the interactive menu:

  1. Select the affected partition (usually the last partition on the disk)
  2. Choose Resize and confirm the new size (usually defaults to all available free space)
  3. Choose Write and confirm with yes
  4. Exit with Quit

📝 cfdisk only changes the partition table, not the data itself. Growing a partition is therefore uncritical — it's just important that the partition being resized is the last one on the disk.

3. Verify the partition size

fdisk -l <pathtomaindevice> #example path: /dev/sda

Check that the target partition (e.g. /dev/sda3) now shows the expected new size.

4. Cross-check with parted (optional)

parted

In the parted prompt:

  1. print — shows the current partition table
  2. As an alternative to cfdisk, you can also resize here using resizepart: enter the partition number, then the new end point (or 100% for maximum size)
  3. quit — exit the program

5. Grow the LVM Physical Volume (PV)

pvresize <pathtonewdevice>

Example: pvresize /dev/sda3

Extends the physical volume to use the newly available space on the partition. Use pvs to verify the new PV size.

6. Grow the LVM Logical Volume (LV)

lvextend -l +100%FREE <pathtolocalpartition>

-l +100%FREE allocates all free space in the volume group to the logical volume. If you only want to allocate part of it, you can use e.g. -L +20G instead.

7. Grow the filesystem

resize2fs <pathtolocalpartition>

Grows the filesystem (ext2/ext3/ext4) to the new size of the logical volume — only this step actually makes the additional space usable by the system.

⚠️ For XFS, resize2fs won't work — use xfs_growfs <mountpoint> instead (note: this takes the mount point, not the device path). You can check the filesystem type with df -T.

8. Verify the result

df -h

9. Reboot

reboot

A reboot isn't strictly necessary since the changes are already active, but it's good practice to confirm the VM comes back up cleanly with the new configuration.

Common pitfalls

  • Wrong partition selected — always check with fdisk -l or lsblk before each step to confirm which device/partition is affected.
  • Not the last partition — a partition can generally only be extended into unallocated space immediately following it.
  • Forgetting the filesystem step — pvresize/lvextend only grow the LVM layers; the filesystem still needs to be extended separately with resize2fs/xfs_growfs.
  • XFS with resize2fs — fails or does nothing useful; use xfs_growfs instead.
  • No backup — always back up before modifying partition tables.
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