How to Increase LVM Disk Size on Proxmox VE: GUI, CLI, and Filesystem Expansion

Proxmox shows the VM a disk of the new size but does not touch the filesystem. This is the main trap: the admin resizes in GUI, boots the VM, and df -h still shows the old size. Expansion goes through three separate steps: increase the logical volume on the host, expand the partition inside the VM, extend the filesystem. Miss any one and the space never appears.

What LVM Means in Proxmox

Proxmox stores VM disks as LVM logical volumes inside a Volume Group. The default pool is called local-lvm. Physical disks are pooled into a Volume Group, volumes for VMs are carved from it. This allows resizing without stopping the physical server.

Step 1: Resize the Disk in Proxmox Web GUI

Select the VM, go to Hardware, find the disk (scsi0 or virtio0), click Resize disk.

Enter the Size Increment - this is a delta, not a final size. Disk was 20G, target is 40G - enter 20G. Click Resize disk. Instant, no VM shutdown needed.

Step 1 (Alt): Resize via Host CLI

# Check VM disk config (101 = VM ID)
qm config 101 | grep scsi

# Add 20G to disk scsi0
qm resize 101 scsi0 +20G

# Verify
qm config 101 | grep scsi

The plus sign is required. This is an increment, not an absolute value.

Step 2: Expand the Partition Inside the VM

SSH into the VM or use Proxmox Console. Check state:

lsblk

Disk shows new size, partition shows old. Expand with growpart:

sudo growpart /dev/sda 1

Install if missing:

sudo apt install cloud-guest-utils

For LVM inside the VM:

sudo pvresize /dev/sda1
sudo lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv

Step 3: Extend the Filesystem

ext4:

sudo resize2fs /dev/sda1

Works on a mounted partition. No reboot needed.

xfs:

sudo xfs_growfs /

XFS needs the filesystem mounted. Argument is mount point, not device.

Verify:

df -h

One-Liner for Ubuntu/Debian

After Proxmox resize, inside the VM:

sudo growpart /dev/sda 1 && sudo resize2fs /dev/sda1

For LVM root:

sudo growpart /dev/sda 3 && sudo pvresize /dev/sda3 && sudo lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv && sudo resize2fs /dev/ubuntu-vg/ubuntu-lv

Partition numbers vary by image. Always verify with lsblk first.

Shrinking: Why Proxmox Blocks It

Proxmox GUI only allows increasing disk size, never decreasing. Shrinking requires manual LVM work and risks data loss. Before any shrink attempt, take a snapshot or backup with vzdump.

Quick Reference