I am trying to add a drive to the existing NAS and then add that empty data to the Datastore? Can anyone help?
Shure, but we definitely need more info about the infraestructura you are currently working with...
For example, what kind of RAID the NAS have, how many disks already configured, type and version of VMFS in the VMware infraestructure..., type of connection (e.g. iSCSI, NFS), any addicional info you could give us.