This article explains where to find instructions on adding backup storage to a VMware UEB appliance.
If you need to add backup storage to your VMware UEB, determine whether the UEB was deployed to an internal disk or to an external NAS or SAN. If you deployed your UEB to a disk that is internal to the hypervisor, add directly attached storage (DAS). If you deployed to an external NAS or SAN, add storage (through the hypervisor) that resides on that external array.
For more information, see the procedures described in To create additional storage for VMware.