Unmounting a datastore is a way of telling the ESXi host that the LUN will no longer be available for any I/O operation, until it is re-mounted. It is recommended to unmount a VMFS datastore before the LUN backing it is unpresented from an ESXi host.
Note
It is advised that you take care of the following before you proceed with the unmount operation:
All the VMs should be migrated off to a different datastore
The datastore should be removed from a datastore cluster
The datastore should remain unmanaged by Storage DRS (SDRS)
Storage I/O Control (SIOC) should be disabled for the datastore
Should not be in use as a vSphere HA heartbeat datastore
A VMFS volume can be unmounted from the vSphere Web Client GUI or using the tools available in the ESXi's CLI. In the How to do it... section of this recipe, we will cover both of these methods.