💾 Proxmox – How to Resize VM Disk for Ubuntu, Windows 10, and Windows Server (Step-by-Step Guide)

Managing virtual machine storage efficiently is a critical skill for any Proxmox administrator. As workloads grow, applications expand, and data accumulates, virtual disks may run out of space. Knowing how to safely resize VM disks without downtime or data loss is essential for maintaining a stable virtualization environment.

In this step-by-step tutorial, you will learn how to:

• ✅ Increase virtual disk size in Proxmox GUI

• ✅ Resize partitions inside Ubuntu VM

• ✅ Extend disk space on Windows 10

• ✅ Expand system volume on Windows Server

• ✅ Avoid common resizing mistakes

• ✅ Maximize storage efficiency without reinstalling VMs

This guide is suitable for both beginners and experienced system administrators managing Proxmox VE in homelab or production environments.

🐧 1️⃣ Resize Disk for Ubuntu VM

Expanding disk space in Ubuntu requires resizing both the virtual disk (Proxmox side) and the partitions inside the operating system.

🔹 Step 1: Increase Disk Size in Proxmox GUI

• Go to VM → Hardware → Hard Disk

• Click Resize Disk

• Enter the number of GB to increase

This adds free space to the virtual disk but does not automatically extend the partition inside Ubuntu.

🔹 Step 2: Install Partition Extension Tool

Inside Ubuntu VM:

This tool allows you to extend partitions safely.

🔹 Step 3: Expand the Partition

Purpose: Expand partition number 3 (/dev/sda3) to take up all the free space on disk /dev/sda.

Expand LVM Physical Volume (PV)

Expand Logical Volume (LV)

This command consumes all available free space from the physical volume.

🔹 Step 4: Expand the Filesystem

Check disk usage first:

If using ext4 (default Ubuntu filesystem):

Verify again:

✅ Ubuntu VM disk resizing is now complete.

🪟 2️⃣ Resize Disk for Windows 10 VM

Windows resizing is simpler but may require third-party tools if partitions block extension.

🔹 Step 1: Increase Disk Size in Proxmox GUI

• Go to VM → Hardware → Hard Disk

• Click Resize Disk

• Enter the number of GB to increase

🔹 Step 2: Install Minitool Partition

Inside Windows 10:

• Install Minitool Partition

• Use Move/Resize to shift system partition to the right

• Extend the size

This allows the system partition to use newly allocated unallocated space.

✅ Windows 10 disk resizing completed successfully.

🖥️ 3️⃣ Resize Disk for Windows Server

Resizing disk on Windows Server is typically easier thanks to built-in management tools.

🔹 Step 1: Increase Disk Size in Proxmox GUI

• Go to VM → Hardware → Hard Disk

• Click Resize Disk

• Enter the number of GB to increase

🔹 Step 2: Extend Volume from File and Storage Services

• Open File and Storage Services

• Go to Volumes → Disks

• Select drive C

• Click Extend Volume

• Enter maximum capacity

Windows Server will expand the volume using available unallocated space.

✅ Windows Server disk expansion is completed.

⚠️ Common Issues When Resizing VM Disks

While resizing is generally safe, administrators may encounter:

• ❌ Partition not detected after resizing in Proxmox

• ❌ LVM not recognizing new space

• ❌ Windows system partition blocked by recovery partition

• ❌ Filesystem not expanding automatically

To avoid issues:

✔ Always backup critical data
✔ Verify disk layout before resizing
✔ Resize filesystem after resizing logical volume
✔ Confirm final capacity with df -h or Disk Management

🚀 Best Practices for VM Disk Management

Proper VM disk management improves:

• Performance

• Storage efficiency

• Resource allocation

• Long-term scalability

Tips for Proxmox administrators:

• Monitor disk usage regularly

• Avoid allocating excessive storage upfront

• Use LVM for flexibility

• Plan storage growth proactively

• Test resizing in lab before production

🎯 Conclusion

In this tutorial, you have learned how to resize VM disks on:

• Ubuntu (LVM + ext4)

• Windows 10

• Windows Server

You now understand both the Proxmox-level disk expansion and the OS-level partition resizing process. Mastering this skill ensures:

✔ Zero unnecessary downtime
✔ Safe storage expansion
✔ Optimized virtual infrastructure
✔ Greater flexibility for growing workloads

With proper VM disk management, your Proxmox environment becomes more resilient, scalable, and production-ready.