FIOS: A Fair, Efficient Flash I/O Scheduler

Flash-based solid-state drives (SSDs) have the potential to eliminate the I/O bottlenecks in data-intensive applications. However, the large performance discrepancy between Flash reads and writes introduces challenges for fair resource usage. Further, existing fair queueing and quanta-based I/O schedulers poorly manage the I/O anticipation for Flash I/O fairness and efficiency. Some also suppress the I/O parallelism which causes substantial performance degradation on Flash. This paper develops FIOS, a new Flash I/O scheduler that attains fairness and high efficiency at the same time. FIOS employs a fair I/O timeslice management with mechanisms for read preference, parallelism, and fairness-oriented I/O anticipation. Evaluation demonstrates that FIOS achieves substantially better fairness and efficiency compared to the Linux CFQ scheduler, the SFQ(D) fair queueing scheduler, and the Argon quanta-based scheduler on several Flash-based storage devices (including a CompactFlash card in a low-power wimpy node). In particular, FIOS reduces the worst-case slowdown by a factor of 2.3 or more when the read-only SPECweb workload runs together with the write-intensive TPC-C.