| Summary: | 碩士 === 國立臺灣大學 === 資訊工程學研究所 === 103 === NAND flash-based SSDs have been regarded as great alternatives of mechanical HDDs due to their impressive performance and low power consumption. Since the architecture of SSD is different from that of HDD, SSD can achieve higher performance by exploiting internal parallelism. Despite of the rich parallelism, current I/O schedulers dispatch I/O requests without considering the loading of each die in the SSD. It aggravates unbalanced loading in SSD so that the parallelism may not be fully exploited. In addition, existing I/O schedulers use anticipation technique, which idles the device for anticipating soon-arriving request, to balance the usage of the SSD between read and write process. However, anticipation technique has negative effect on performance of the SSD. This thesis proposes a cross-layer I/O scheduler, which utilizes the feature of PCI Express device to enable the host system to access the mapping table of SSD. According to the information of mapping table, our cross-layer scheduler maintains a loading table in the host system to deal with unbalanced loading problem and selectively relax the limitation of fairness to maximize the parallelism of the SSD. Experiment results demonstrate our cross-layer scheduler can improve about 20% average I/O response time compare to conventional I/O scheduler which is not aware of the internal parallelism of SSD. Furthermore, we can achieve about 23% improvement compare to state-of-the-art fairness-oriented scheduler but without losing fairness.
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