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 charac- terize storage systems: energy efficiency, durability, and more are becoming equally  important. We posit that one must evaluate storage systems from a monetary cost per- spective as  well as performance.  We believe that cost should consider the workloads used over the storage sys-  tems’ expected lifetime.  We designed and developed a versatile hybrid storage system under Linux  that com- bines HDD and SSD. The SSD can be used as cache or as primary storage for hot data. Our  system includes tun- able parameters to enable trading off performance, en- ergy use, and  durability. We built a cost model and eval- uated our system under a variety of workloads and pa-  rameters, to illustrate the importance of cost evaluations of storage systems.