Simulation and performance analysis of the ECMWF tape library system

Improvements in hardware and software have enabled magnetic disks to become an alternative to tape in backup environments. Nevertheless, even considering its slow access times, tape is still part of most hierarchical storage management strategies. The main reasons are cost-effectiveness, long lifetimes, and that tape, continually improved, keeps up with magnetic disks in terms of capacity. The performance of tape libraries, however, has been scarcely analyzed in the literature. In this paper, we present a tape library simulator and analyze workload traces of the European Centre for Medium-Range Weather Forecasts. Optimizing the cartridge management, we show that the load latency can be reduced by a factor of 2.1 and the number of load operations by 2.5, compared to standard library settings. Furthermore, we present eviction and placement strategies, which can additionally lower the load latency by 20%, achieving the same performance level with considerably fewer drives.