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Proxmox VM Disk Resize Guide

This guide covers how to resize a VM disk in Proxmox and extend the filesystem within the VM to use the additional space.

Prerequisites

  • VM is powered off (recommended) or has hot-plug support enabled
  • Backup of the VM (strongly recommended before any disk operations)
  • SSH access to the VM
  • Root/sudo access on the VM

Step 1: Resize Disk in Proxmox

  1. In Proxmox web interface, navigate to your VM
  2. Go to Hardware tab
  3. Select the disk you want to resize
  4. Click Resize disk
  5. Enter the additional size (e.g., +48 to add 48GB)
  6. Click Resize disk
  7. Restart the VM if it was powered off

Step 2: Verify Disk Size in VM

SSH into your VM and check the current disk usage:

df -h

Check if the disk size has increased:

sudo fdisk -l /dev/sda

Step 3: Extend Partition (if using LVM)

Check partition table:

sudo parted /dev/sda print

If there's unallocated space, extend the partition:

sudo parted /dev/sda resizepart 3 100%

When prompted:

  • Fix/Ignore? → Type Fix
  • Partition number? → Type 3 (or the appropriate LVM partition number)
  • End? → Type 100%

Step 4: Extend Physical Volume

Resize the physical volume to use the extended partition:

sudo pvresize /dev/sda3

Verify the change:

sudo pvdisplay

Step 5: Extend Logical Volume

Extend the logical volume to use all available space:

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

Replace ubuntu--vg-ubuntu--lv with your actual logical volume path (visible in df -h output).

Verify the change:

sudo lvdisplay

Step 6: Resize Filesystem

Resize the filesystem to use the extended logical volume:

sudo resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv

Step 7: Verify Results

Check the final disk usage:

df -h

You should now see the full allocated space available.

Common Issues and Solutions

Issue: "No space left on device" errors persist

Solution: Services may need to be restarted after disk expansion:

sudo systemctl restart [service-name]

Issue: Partition table shows wrong size

Solution: Reboot the VM to ensure the kernel recognizes the new disk size:

sudo reboot

Issue: LVM commands fail

Solution: Check if the correct physical volume device is being used:

sudo pvdisplay
sudo vgdisplay
sudo lvdisplay

Alternative: Non-LVM Systems

If your system doesn't use LVM, the process is simpler:

  1. Extend partition: sudo parted /dev/sda resizepart 1 100%
  2. Resize filesystem: sudo resize2fs /dev/sda1

Safety Notes

  • Always backup your VM before performing disk operations
  • Test in a non-production environment first
  • Partition operations can be destructive - double-check device names
  • Consider using VM snapshots before starting the resize process

Verification Commands

Use these commands to verify each step:

# Check disk hardware size
sudo fdisk -l /dev/sda

# Check partition table
sudo parted /dev/sda print

# Check physical volumes
sudo pvdisplay

# Check volume groups
sudo vgdisplay

# Check logical volumes
sudo lvdisplay

# Check filesystem usage
df -h