The Device page of a job's properties lets you select the devices that will be used. You may select as many devices as you wish for use in a job and Yosemite Server Backup will use the devices as efficiently as it can.
You can view the available devices by either a Device view or by Network view by selecting the appropriate tab.
The Device view allows you to locate devices according to their class — for example, tape drives. Since Yosemite Server Backup can read and write CDs and DVDs (optical media) a large domain may have dozens of devices, many of which are optical devices. This view make it simple to locate the tape drives or libraries in your network. Each class of device is represented as a node at the top of a tree hierarchy. By checking the box next to a class of device you are telling Yosemite Server Backupto use any device of that class it can find available when the job runs. This is a powerful concept because it allows you to add additional devices to your network and to your jobs without having to reconfigure your jobs. If you expand the class by clicking the + next to the class name you will see the names of each device of that class. Expanding the name will show you which machine the device is attached to. Selecting a specific device will ensure that only that device will be used in the job.
The Network view presents the same map of your devices but from a different perspective. At the top of the hierarchy is the Network. Next to each element in this list is a set of checkboxes representing the supported classes of devices. Selecting the Tape Devices box next to the Network configure the job to use all tape drives in the network at the time the job runs. Under the Network you will see machines. Selecting a class of devices next to a machine will limit the job to use only that class of device on that machine. Finally, when the machine is expanded, all connected devices are displayed. There will be a checkbox in the column appropriate for the class of device. Checking that box will select just that device for use with the job.
NOTE: New devices added to the network after a job has started running will not be available to the job until the next run.