Proxmox P22 – Disk Passthrough Guide

Assign a Physical Disk to Your Virtual Machine on Proxmox 9 (Step-by-Step)

Managing storage efficiently is a critical skill for any Proxmox administrator. In this tutorial, you will learn how to perform Disk Passthrough in Proxmox VE (PVE) and assign a physical disk directly to your virtual machine. This guide follows a safe, production-ready approach and works perfectly for home labs as well as enterprise environments.

Disk passthrough allows a VM to directly control a physical disk as if it were an internal hard drive. This method improves flexibility, enhances storage management, and ensures data portability between Proxmox hosts.

If you are running Windows, TrueNAS, ZFS, or any storage-focused VM, this technique is a game-changer.

📌 What Is Disk Passthrough in Proxmox?

Disk passthrough means assigning a physical disk or storage device directly to a VM (virtual machine). The VM will manage that disk independently — including partition creation, RAID configuration, and filesystem management.

➤ Example use case:
Assign the entire /dev/sdc drive to a VM running ZFS, TrueNAS, or Windows so the VM can create partitions and manage storage natively.

This approach ensures that data remains on the physical disk — not inside a virtual disk file.

🎯 1.1.1 Objectives

Our lab scenario:

• Proxmox A: Install a Windows 10 VM (or any OS) with drive C: (Operating System)
• Assign an additional physical disk /dev/sdb (passthrough) → VM sees drive D:
• Store data on drive D:
• If Proxmox A fails, move /dev/sdb to Proxmox B
• Create a new VM → passthrough /dev/sdb → VM still sees drive D: and all data remains intact

This setup ensures maximum portability and data protection.

🔧 1.1.2 Steps to Passthrough a Physical Disk (Example: /dev/sdb)

🔹 Step 1: Identify the Physical Disk

On Proxmox A, run:

Example output:

⚠️ Important:
Do NOT use /dev/sdb directly because disk names can change after reboot.

Instead, use the persistent disk ID:

Example:

Always use the /dev/disk/by-id/ path for stability and reliability.

🔹 Step 2: Modify VM Configuration

Suppose:

• VM ID: 100 (Windows 10)
• Disk path: /dev/disk/by-id/ata-QEMU_HARDDISK_QM00005

Open the VM configuration file:

Add the following line:

If you prefer SATA:

Explanation:

• cache=writeback improves performance (similar to virtual disk behavior)

• Use cache=none if maximum data integrity is required

• SCSI is recommended

• SATA is used when compatibility with older operating systems is required

• IDE is slow

• VirtIO requires Windows driver installation

🔹 Step 3: Restart the Virtual Machine

After rebooting the VM:

• Windows 10 will detect the new disk as an additional drive (drive D:)
• If it is a new disk → format it
• If it already contains data → Windows will immediately mount and recognize it

Your disk passthrough is now successfully configured.

🔄 1.1.3 Restore Passthrough Disk on Another Proxmox Host

If Proxmox A fails:

1. Remove the passthrough disk (/dev/sdb) from machine A

2. Connect it to Proxmox B

3. Verify disk ID using:

    

   lsblk ls /dev/disk/by-id/

4. Create a new Windows VM (or restore from backup if available)

5. Edit the new VM .conf file and add the passthrough line exactly as before

When the VM boots:

→ Windows will detect drive D:
→ All data remains intact
→ No reconfiguration required inside Windows

Because the data resides on the physical disk itself — not inside a virtual disk file.

⚠️ 1.1.4 Extremely Important Notes

These precautions are critical for production environments.

🧪 Quick Verification After Passthrough

Inside the VM:

• Open Disk Management
• Check for drive D:

If first time use → format
If existing data → mount and use immediately

🚀 Final Thoughts

Disk Passthrough in Proxmox 9 provides powerful flexibility for managing physical storage within virtual machines. It is ideal for:

• TrueNAS deployments

• ZFS storage VMs

• Database servers

• File servers

• Production workloads

• Migration scenarios between Proxmox hosts

By correctly using /dev/disk/by-id and modifying the VM configuration file safely, you ensure data integrity, portability, and high performance.

Mastering disk passthrough will significantly improve your Proxmox infrastructure management skills and give you full control over VM storage architecture.