Lightning Server will monitor the USB drive plugged into a Lightning device and do an initial scan of the USB drive to find all music files it supports. If the USB drive has never been plugged into current Lightning device, it may take a while to finish the scan, as the scan speed depends on how many files are on USB drive.
Network Share Folder:
After you type the network share folder path into the Lightning DS along with the Authorized Account / Password combination, Lightning Server will do the initial scan for the first time as soon as you mount the folder. You will be able to play your Network Share Content when the scan is done.