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Backing Up to an External Disk in Proxmox and Restoring on Another Server

Purpose

In this guide, we will explain:

• Backing up to an external SSD on a Proxmox server (PRX-1)
• Safely removing the SSD
• Restoring the backup on another Proxmox server (PRX-2)

We will walk through these steps completely and securely.

This method is especially ideal for:

• Offline migration
• Disaster recovery
• Server migration
• Air-gapped backups

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1️⃣ BACKUP PROCESS ON PRX-1

Step 1 – Formatting the External Disk

First, check if the disk is visible to the system:

lsblk

The disk may appear as /dev/sdf or /dev/sdf1.

Format the disk as ext4:

mkfs.ext4 /dev/sdf

⚠️ Note: Formatting will erase all data on the disk.

Step 2 – Creating the Mount Directory

mkdir -p /mnt/usbbackup

Step 3 – Mounting the Disk

mount /dev/sdf /mnt/usbbackup

Verify:

df -h | grep usbbackup

Step 4 – Adding the Storage via Proxmox UI

Mounting alone is not sufficient. The disk must also be added as storage in Proxmox.

1. Datacenter
2. Storage
3. Add → Directory

Fill in the fields as follows:

Field	Value
ID	usb-backup
Directory	/mnt/usbbackup
Content	✔ VZDump backup file
Nodes	PRX-1

Step 5 – Taking the Backup

Node → VM → Backup → Backup now

• Storage: usb-backup
• Mode: Snapshot
• Compression: zstd (recommended)

The backup file will be created under:

/mnt/usbbackup/dump/

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Step 6 – Removing the Storage from Proxmox (IMPORTANT)

Before physically disconnecting the disk:

Datacenter → Storage → usb-backup → Remove

• This does NOT delete the disk.
• It only removes it from Proxmox configuration.

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Step 7 – Safely Disconnecting the Disk

sync
umount /mnt/usbbackup

Verify with:

df -h

The disk should no longer appear in the mounted list.

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2️⃣ RESTORE PROCESS ON PRX-2

Step 1 – Connect the External SSD to PRX-2

lsblk

Step 2 – Create the Mount Directory

mkdir -p /mnt/usbbackup

Step 3 – Mount the Disk

mount /dev/sdf /mnt/usbbackup

Step 4 – Add Storage via Proxmox UI

Datacenter → Storage → Add → Directory

Field	Value
ID	usb-backup
Directory	/mnt/usbbackup
Content	✔ VZDump backup file
Nodes	PRX-2

Step 5 – Restore Process

Node → Storage → usb-backup → Select backup file → Restore

• VMID: Same or new ID
• Target Storage: Where VM disks will be stored

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Important Notes

✔ Do Not Unmount Before Removing Storage

Otherwise, Proxmox may show “storage not available” errors.

✔ Always Use sync Before Removal

sync

✔ ext4 is Recommended

ext4 is the most stable file system for external backup disks.

✔ emergency_ro Error

If you see:

emergency_ro

The disk has switched to read-only mode due to filesystem errors. Run fsck to repair it.

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With this method:

• Secure offline backups can be taken
• Manual migration between Proxmox servers is possible
• Disaster recovery scenarios can be implemented
• Air-gapped backups can be maintained

This procedure can be safely applied in production environments.