Backup Copy Fails on Proxmox VM

Product version: 11.0

Last modified: 04 June 2025

Problem

The Backup Copy job for a Proxmox VM fails with the following error:

Data size mismatch

This issue typically occurs when there is a mismatch between the expected disk size and the actual size detected during the Backup Copy process. As a result, the Backup Copy job fails.

Solution

To resolve this issue, follow these steps:

  1. Rescan the virtual disks on the Proxmox host. Open the Proxmox shell and run the following command:

qm disk rescan

  1. Navigate to Settings > Inventory, locate your Proxmox item and click Refresh.

  2. Open the Backup job that includes the affected Proxmox VM and unmap or remove the existing Backup Object for this VM.

  3. Run a new Backup job for the affected Proxmox VM. This will create a fresh Backup Object aligned with the updated VM configuration.

  4. Edit the Backup Copy job and select the newly created Backup Object as the source.

  5. Rerun the Backup Copy job. Ensure the job proceeds successfully without the data size mismatch error.