This type of error is usually related to inconsistent backup chains or snapshot issues. Here are a few things to check:
Verify the VM still exists and is healthy
- If the VM was deleted, recreated, or its UUID changed, the backup job may fail with read errors like this.
- Make sure the VM referenced in the backup task still matches the current VM in the environment.
Check for broken or missing snapshots / backup chain
- If previous snapshots or backup files were manually deleted or cleaned up abnormally, the system won’t be able to calculate incremental data.
- Review the VM snapshot status for any inconsistencies.
Validate backup storage availability
- If the backup repository is on network storage (NFS, iSCSI, etc.), temporary disconnections or permission issues can prevent access to existing backup data.
- When the backup data can’t be read, the incremental size calculation will fail.
Recommended resolution
- After confirming the VM and backup storage are healthy, try running a full backup to rebuild the backup chain.
- If the issue persists, consider cleaning up the affected backup records and recreating the backup job.
This issue is fairly common in environments where backup storage is unstable or backup chains are interrupted. In most cases, checking the VM state and backup repository will lead you to the root cause.
