TReqS: The Tape REQuest Scheduler

TReqS is a new layer in the storage infrastructure at CCIN2P3 controlling the read operations for data stored on tapes in HPSS (a HSM) by centralizing all requests. The development and deployment of TReqS at CCIN2P3 has brought major advances in data access services on several aspects. First, by sorting and scheduling tape mounts, we radically reduce the waiting time due to media movements in the tape library. Second, in a mutualised environment where tape drives are globally available to all users, TReqS ensures the fair share of the drives. Finally, TReqS softens the impact of unpredictable grid jobs and transfers on the actual tape library and efficiently masks the data access complexity to the end user.