In this thesis, We tried to address the issue of SSD performance towards random write workload. We propose a buffer management scheme which tries to access all elements of an SSD in parallel by utilizing its architectural design. The basic idea is to buffer requests into DRAM, reshape the write access pattern and create a group of requests from which each request targets individual element. EPO exploits element-level concurrency and significantly reduces the mean response time and improves the throughput. One very important thing to take care about using cache is to save all the data in cache when power failure occurs, but there are other algorithms can be developed to minimize the number of writes to flash when power failure happens. Comparing with non-volatile RAM and enhanced FTL engine developing approaches, EPO has several advantages: (1) its hardware cost is low as it requires very small size of cache, (2) it requires trivial change in the FTL and it’s very easy to implement, and (3) the algorithm is very simple to implement in real applications. EPO outperforms other three algorithms including LRU and BPLRU. Especially, EPO improves in mean response time by 63.8% and 49.5% than that of LRU and BPLRU when SSD is in its default configuration (cache size 8MB, page size 4KB, number of elements 48).
In my current thesis, we assumed each write request is of one page size and modified the size of each request in all traces we used, to one page. Another important assumption we made is, each requested LBA is page aligned. We are planning to extend my experiments with unaligned LBA and request size not equals to one page as a future work. We are
planning to implement full cache management policy inside the SSD extension by Microsoft research [28] as this extension does not provide any cache management function. Further improvement can be made by exploiting the SSD architecture even deeper and accessing planes in parallel, interleaving between read and write requests. We are also going to develop SSD disk array level cache management schemes not only to improve the random write performance but also to increase SSD life span.
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