為了增加MLC flash memory的整體效能，會把SSD 中一部分的MLC block 轉換成pseudo SLC block，能讓這些block 能夠有一般SLC block的效能，因為此時只有兩個threshold voltage status，所以寫入速度會比有四個threshold voltage status 的MLC block 快上許多。然而pseudo SLC block藉由捨去一半的空間來加速，卻會導致整體write amplification上升。為了解決這個問題，我們更改flash 的encoding scheme 來讓pseudoSLC block可以不用捨棄一半的資料且依然能保有其高效能的寫入速度，同時我們提出兩種模型，分別能夠改善average write response time 和write amplification，可以依照使用者的偏好來決定使用哪種模型，增加使用上的彈性。經由我們的實驗可顯示出在average write response time 方面，我們的方法最大可改善14%；在erase count 方面，最大可改善59%；而在write amplification 方面，我們的方法最大可改善12%。

In order to increase the overall performance of MLC flash memory, some MLC blocks in the SSD will be converted into pseudo SLC blocks. Therefore, these blocks can have the performance of normal SLC blocks. Because there are only two threshold voltage status at this time, the writing speed will be much faster than the MLC block with four threshold voltage status. However, the pseudo SLC block is accelerated by cutting down half of the space. Thus, it will cause the overall write amplification to increase. In order to solve this problem, we changed the encoding scheme of the flash memory so that the pseudo SLC block does not need to discard half of the data and still keeps high-performance writing speed. We propose two models that improve the average write response time or write amplification. User can decide which model to use according to their preference. According to our experiments, it can be shown that in average write response time, our method can improve up to 14%; in erase count, our method can improve up to 59%; and in write amplification, our method can improve up to 12%.

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