RADIR: Lock-free and wait-free bandwidth allocation models for solid state drives

Novel applications such as micro-blogging and algorithmic trading typically place a very high load on the underlying storage system. They are characterized by a stream of very short requests, and thus they require a very high I/O throughput. The traditional solution for supporting such applications is to use an array of hard disks. With the advent of solid state drives (SSDs), storage vendors are increasingly preferring them because their I/O throughput can scale up to a million IOPS (I/O operations per second). In this paper, we design a family of algorithms, RADIR, to schedule requests for such systems. Our algorithms are lock-free/wait-free, lineariz-able, and take the characteristics of requests into account such as the deadlines, request sizes, dependences, and the amount of available redundancy in RAID configurations. We perform simulations with workloads derived from traces provided by Microsoft and demonstrate a scheduling throughput of 900K IOPS on a 64 thread Intel server. Our algorithms are 2-3 orders of magnitude faster than the versions that use locks. We show detailed results for the effect of deadlines, request sizes, and the effect of RAID levels on the quality of the schedule.