Delete Datastore

Hi gurus

I want to delete a datastore but I am facing the "datastore in use" error, I have checked that no one VM has an iso pointing to this datastore, all VM has been migrated to another Datastore, but there is still a folder that has  some files recently modified

Vphere.HA and some naa  I have a protectedfile on vsphere.HA and some spotfile on the naa. folder.

1) do I have to unmount the datastore first before I an even think of deleting the Datastore all together

2) How do I find out what is still using the datastore so I can get rid off it and delete this datastore .

Thanks a bunch