Abstract-Personal storage is a mainstream service used by millions of users. Among the existing alternatives, Friend-toFriend (F2F) systems are nowadays an interesting research topic aimed to leverage a secure and private off-site storage service.However, the specific characteristics of F2F storage systems (reduced node degree, correlated availabilities) represent a hard obstacle to their performance. Actually, it is extremely difficult for a F2F system to guarantee an acceptable storage service quality in terms of transference times and data availability to end-users. In this landscape, we propose to resort to the Cloud for improving the storage service of a F2F system.We present FriendBox: a hybrid F2F personal storage system. FriendBox is the first F2F system that efficiently combines resources of trusted friends with Cloud storage for improving the service quality achievable by pure F2F systems.We evaluated FriendBox through a real deployment in our university campus. We demonstrated that FriendBox achieves high transfer performance and flexible user-defined data availability guarantees. Furthermore, we analyzed the costs of FriendBox demonstrating its economic feasibility.