利用FTL元資料日誌系統修復發生異常斷電的快閃記憶體儲存裝置

Abstract

近年來手持式NAND flash儲存裝置應用度越來越廣泛，並由於隨插即用特性使得使用者資料流通性更加便利，但隨即衍生的問題即是異常斷電，因為無法預測使用者何時會拔掉flash儲存裝置，這意味著FTL有可能在做任何快閃記憶體操作時斷電，從而毀損使用者資料或者FTL的元資料，因此需要發展一種方法可以用來確保FTL的元資料不會因為異常斷電而發生毀損。本論文提出一種新的FTL元資料日誌系統，來面對快閃記憶體儲存裝置發生異常斷電的狀況，簡單來說:在快閃記憶體獨立一個特定的區塊，稱之為”Tracker”，”Tracker”會紀錄每一筆AWOP的相關元資料，當發生異常斷電時，FTL可以透過”Tracker”內的記錄重建FTL的元資料，使FTL有元資料的完整性。由於"Tracker"紀錄AWOP的元資料需要額外的頁寫入操作，所以無可避免會造成寫入效能損失，實驗結果顯示對原先FTL的寫入效能還保有92%，且修復時間比起傳統FTL需要掃描所有快閃記憶體明顯少上許多。

In recent years, the application of portable NAND flash storage devices is being widely used. Thanks to Plug-and-Play feature makes users’ data liquidity more convenient. But this feature derivatives problem is power failure, since it unable to predict when users will plug out this storage device. That means FTL might power failure during any flash operation to destroy users’ data or FTL metadata. For this reason, we need to develop a method to ensure FTL metadata won’t be destroyed because of power failure occur. This paper presents a FTL metadata journaling method to solve flash device abnormal power failure situation. To be brief to say: at a special block of NAND flash memory , which called “Tracker “. It will record every AWOP related metadata when power failure. FTL can use “Tracker “records to re-build FTL metadata make FTL keep metadata integrity. Due to “Tracker “records AWOP metadata need additional page to write, therefore inevitably will cause write performance lost. The experiment result shows compare to traditional FTL, " Tracker " write performance still remain 92% , and the spent time of use Tracker to rebuild metadata lesser than traditional FTL method.