Two different issues are possible:
I. When trying to remove a protection domain containing the virtual machines, which are being backed up by Veeam Availability for Nutanix backup appliance, you may get the following message:
Specified protection domain has third-party backup snapshot(s)
II. You may start receiving the following warning in your cluster for a few protection domains or virtual machines:
Aged third-party backup snapshots present
Veeam Availability for Nutanix backup proxy appliance creates and keeps snapshots for each virtual machine in the backup job for the change block tracking purposes. It is not possible to remove a protection domain containing such snapshots. The default warning threshold for the third-party snapshots is equal to seven days, therefore you may start receiving warnings if any of the third-party snapshots is older than this threshold.
I. To resolve the first issue you need to delete the snapshots first. The snapshots will be automatically dismissed for the virtual machine once you remove the entire backup policy or stop processing the virtual machine by the backup job. You may follow the next steps to achieve the latter:
These actions will delete the third-party snapshots created by our backup proxy appliance for these machines and will allow you to remove the protection domain finally.
II. To resolve the second issue, you may increase the warning threshold in your cluster or change the schedule of your backup job to have it running within this threshold. You may also safely ignore the warning.