To modify the visibility of a volume:
Select the desired volume in the local menu, then click the Show button (to make it visible) or the Hide button (to make it invisible).
The Visibility panel allows you to act on the visibility state of a volume, folder or file.
Select the desired volume in the local menu, then click the Show button (to make it visible) or the Hide button (to make it invisible).
Click the "Show Folder" button to make it visible or "Hide Folder" to make it invisible, then in the dialog box that appears, select the desired folder.
Note: These two buttons can possibly influence the visibility of a volume.
Click the "Show File" button to make it visible or "Hide File" to make it invisible, then in the dialog box that appears, select the desired file.
Warning: All these operations relaunch the Finder. Verify that no operation is in progress (copying, moving, burning, and emptying trash).