Dear
First if your database SQL server and you want to take a backup on disk or USB or EXT HDD so to take a full backup throw db13 u must do as follow:
1- connect to ur SQL server management studio .. note: almost ur server name: localhost
2-under localhost choose==>server object==>Backup Devices then right click on it and choose new backup device.
3-Device name ( must be with no spaces ) here is ur issue must be one word***
4-choose ur file path then click on ok and close it
5- stop and start your sap system to read your new configuration from database
6-go throw db13 and chose full database backup
7- you will find ur new device chose it then uncheck any parameters related to tape then click on execute Immediately .
i hope this will help you or anyone