記錄式快閃記憶體儲存系統之設計與實做

Abstract

快閃記憶體有許多吸引人的特徵，例如體積小，重量輕，不揮發性，耐撞性和低耗電量。這些特徵使得快閃記憶體相當適合用在個人通訊設備還有嵌入式多媒體系統上，如MP3撥放器和機上盒(Set-top box)。因為快閃記憶體在覆寫資料前需要先抹除區塊。這個動作是相當耗時間跟能量的。除此之外，快閃記憶體區塊的抹除次數有一定的限制。因此，要設計一個有效率，並以快閃記憶體為基礎的儲存系統變得相當具有挑戰性。為了減少抹除快閃記憶體區塊的次數，前人提出了許多資料管理的方法。但是這些方法當中，有些會產生區塊抹除次數不平均的問題，另一些則需要很長的掛載時間。 因此，我們提出了一項新的快閃記憶體資料管理方法。它加了一塊隨機存取記憶體(RAM)來當做快閃記憶體的延伸。除此之外，我們也提出了一個新的資料群集方法（Dynamic data clustering with extra buffer region）來管理我們快閃記憶體裡頭的資料。並且我們也設計新的資料擺放（Data layout）使得我們的快閃記憶體儲存系統可以更有效率的執行。在我們的方法裡頭，經常性的資料更新是在隨機存取記憶體中進行。因此抹除快閃記憶體區塊的次數便會減少。實驗結果顯示，我們的方法可以減少45%~95% 的抹除次數，也因而能延長快閃記憶體的使用期。除此之外，我們也確保可以平均的抹除每一個快閃記憶體區塊。

Flash memory has many attractive features such as small, light weight, non-volatility, shock-resistant and low power consumption. These features are good for personal communication devices and embedded multimedia systems like MP3 player and set-top boxes. However, the erasing-before-overwriting characteristic of flash memory makes the design of flash-based storage systems become challenging. The erase operations are slow and energy-wasted. Moreover, the number of erase times is also limited. To reduce the number of erase operations and evenly wear flash memory, many data management approach were proposed. However, some of them have the uneven-wearing problem on data blocks, while others such as JFFS and JFFS2 need a long mounting time. Therefore, we propose a new data management approach for flash memory that uses an additional RAM buffer as the extension of the flash. Besides, we design a new data clustering method, Dynamic data clustering with Extra Buffer region (DEB), to manage the data in the flash memory. Besides, we design a new data layout for the flash memory to make our storage system more efficient. In our approach, hot data is usually updated in the RAM buffer in order to reduce the number of erase operations. Performance results show that the number of erase operations can be reduced by 45%~95%, flash memory lifetime is prolonged, and even wearing is ensured.