Open the DR4100 web interface and select 'Containers' I have chosen to edit the default "backup" container but you can create a new on if you wish.
Set the connection type to Rapid Data Access (RDA) as show below.
Next, select 'Clients' from the menu, select the RDA tab and click Edit Password in the top left.If you don't see this available, click the CIFS tab and RDA again. Seems to be an interface bug. Select the client type as RDA and enter a secure password.
Open the vRanger interface, selecting My Repositories, find Dell Rapid Data Access (RDA) at the bottom and select 'Add'
Enter a name, I have used DR4100, enter the IP address of the DR4100 on the LAN, enter the backup_user as the username and enter the password you set in the previous step.
Click OK, vRanger will check access to the DR4100 and close the dialogue box. You have finished and can now use the DR4100 as a backup target when creating a new job. I got over 200 MBps in my test backup with Hyper-V 2012 R2.