On the Importance of Evaluating Storage Systems' $Costs

Modern storage systems are becoming more complex, combining different storage technologies with different behaviors. Performance alone is not enough to characterize storage systems: energy efficiency, durability, and more are becoming equally important. We posit that one must evaluate storage systems from a monetary cost perspective as well as performance. We believe that cost should consider the workloads used over the storage systems' expected lifetime. We designed and developed a versatile hybrid storage system under Linux that combines HDD and SSD. The SSD can be used as cache or as primary storage for hot data. Our system includes tunable parameters to enable trading off performance, energy use, and durability. We built a cost model and evaluated our system under a variety of workloads and parameters, to illustrate the importance of cost evaluations of storage systems.