for removing a data storage and add it again this solution is ok:

 1. Use the Storage resource tab, tree mode
2. Select the storage domain in the main tab
3. In the details pane at bottom select datacenter tab
4. Select the DC where the storage domain is active
5. Select Maintenance link
6. Select Detach link to detach from the data center.

Now you don't see any more the storage domain in storage resource tab.
7. Go to system --> Storage
and the storage domain now in in an unlinked state
8. Select the storage domain and choose "remove"
9. Select a host from the list.
10. Click OK to remove the storage domain and close the window.

best regards

seighalani