PDL Abstract
IODA: A Host/Device Co-Design for Strong Predictability Contract on Modern Flash Storage
SOSP โ21, October 26-29, 2021, Virtual Event, Germany.Huaicheng Li^*, Martin L. Putra*, Ronald Shi*, Xing Lin†, Gregory R. Ganger^, Haryadi S. Gunawi*
^Carnegie Mellon University
*University of Chicago
†NetApp
http://www.pdl.cmu.edu/
Predictable latency on flash storage is a long-pursuit goal, yet, unpredictability stays due to the unavoidable disturbance from many well-known SSD internal activities. To combat this issue, the recent NVMe IO Determinism (IOD) interface advocates host-level controls to SSD internal management tasks. While promising, challenges remain on how to exploit it for truly predictable performance.
We present IODA, an I/O deterministic flash array design built on top of small but powerful extensions to the IOD interface for easy deployment. IODA exploits data redundancy in the context of IOD for a strong latency predictability contract. In IODA, SSDs are expected to quickly fail an I/O on purpose to allow predictable I/Os through proactive data reconstruction. In the case of concurrent internal operations, IODA introduces busy remaining time exposure and predictablelatency-window formulation to guarantee predictable data reconstructions. Overall, IODA only adds 5 new fields to the NVMe interface and a small modification in the flash firmware, while keeping most of the complexity in the host OS. Our evaluation shows that IODA improves the 95ยฑ99.99๐กโ latencies by up to 75ร. IODA is also the nearest to the ideal, no disturbance case compared to 7 state-of-the-art preemption, suspension, GC coordination, partitioning, tiny-tail flash controller, prediction, and proactive approaches.
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