Datastore deletion fails with "The Resource is in Use" error

Products

• VMware vSphere ESXi

Issue/Introduction

• Deletion of a Datastore from the vCenter UI with the following error :
  Operation failed!
The Resource '#####' is in Use.

• There are no registered VMs present on the Datastore.

Environment

• VMware vCenter Server 8.x
• VMware vCenter Server 7.x

Cause

Any active objects residing on the Datastore will prevent the deletion process from completing successfully.

Resolution

Before a Datastore can be removed, all active objects (VMs, VM templates, ISOs etc.)  stored on it must be cleared. To ensure the same, please follow the steps outlined below :

1. Place the Datastore in maintenance mode.
2. If the Datastore fails to enter into maintenance mode, it is confirmed that there is another active object in the Datastore which will need to be removed.
3. Remount the datastore and navigate to the VM & VM templates sections where active templates maybe present.
4. Remove or move the template to a different Datastore. 
5. Datastore should now successfully move into maintenance mode and unmount should succeed.

Additional Information

Remove VMFS Datastores