This article explains how to list every filename and usage on a datastore.
VMware vSphere ESX
VMware vSphere ESXi
Since vSphere Client is not able export a list of filename and usage on a datastore, it's recommended to use command from shell such as ls or du.
# Examples
du -a /vmfs/volumes/<datastore_name>/
ls -liR /vmfs/volumes/<datastore_name>/