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This paper presents a cross-layer co-design approach to reduce SSD read response latency. The key is to cohesively exploit the NAND flash memory device write speed vs. raw storage reliability trade-off at the physical layer and run-time data access workload variation at the system level. Leveraging run-time data access workload variation, we can opportunistically slow down NAND flash memory write speed and hence improve NAND flash memory raw storage reliability. This naturally enables an opportunistic use of weaker error correction schemes that can directly reduce SSD read access latency. We develop a disk-level scheduling scheme to effectively smooth the write workload in order to maximize the occurrence of run-time opportunistic NAND flash memory write slow down. Using 2 bits/cell NAND flash memory with BCH-based error correction correction as a test vehicle, we carry out extensive simulations over various workloads and demonstrate that this developed cross-layer co-design solution can reduce the average SSD read latency by up to 96%.
Date of Conference: 17-19 Aug. 2010