在最近幾年，快閃記憶體已經被廣泛作為儲存裝置，應用到嵌入式系統、行動裝置、可攜式播放器、甚至是桌上型電腦上。但快閃記憶體具有不少迥異於傳統磁碟的特性，特別是「erase-before-write」，因為快閃記憶體無法直接在原區塊做資料複寫，那會嚴重地降低效能。此外，快閃記憶體的刪除、寫入也有次數限制。因此，一種被稱為「快閃記憶體轉譯層（Flash Translation Layer, FTL）」的機制被提了出來。經由FTL的協助，快閃記憶體除了可以隱藏掉上述的缺點外，還可以模擬出與傳統區塊裝置一致的介面。
近幾年也有許多 FTL 被提出來，這些 FTL 都有各自的特色，當然他們也存在著作者未曾提及的缺點。在此篇論文中，我們收集了各式各樣工作環境下的磁碟存取記錄，並根據2個著名採用混合式映對的快閃轉譯層演算法（FAST、LAST）建立了FTL模擬器，用來模擬 FTL 執行過程，並分析各個數據。
由實驗結果我們不僅確認了FAST與LAST提出的技術能夠正確並有效的運作。此外，我們檢驗了其他研究者對於FAST只有單獨一個SW log block而表現不好的主張。我們也驗證驅動程式與FTL之間位址轉換的問題無論對於FAST抑或是LAST而言，這個問題確實明顯地影響了FTL的效能表現。

In recent years, flash memory has been widely used as storage in embedded system, mobile device, portable media player, desktop PC, and even enterprise servers. However, flash has different properties from conventional magnetic storage, especially in erase-before-write, i.e. a flash page cannot be directly updated in the same location, and that will cause significant performance penalty. Besides, a flash block has a finite number of erase cycles. Thus, a software mechanism, called flash translation layer (FTL), was proposed to hide those disadvantages of flash memory and provide a block-device-like interface for the system.
There are many FTLs proposed in the last years. The FTLs have different features, and they certainly have their own drawbacks the authors did not mention. In this work, we built 2 outperformed hybrid FTL simulators, and collected all kinds of workload. Our work provides a trace-driven performance study of all kinds of workload on FTL.
Our empirical works confirmed the techniques the 2 FTLs proposed. We also verified that other researches argue that FAST has only one SW log block could not handle concurrent write efficiently. And the page-aligned problem is also evaluated in our work, and, the problem significantly affects the cleaning cost no matter on the FAST or the LAST.

[1] J. Axboe, A. D. Brunelle, N. Scott, and B. Zoetekouw. blktrace(8) - Linux man page. Available: http://linux.die.net/man/8/blktrace
[2] K. Bates and B. McNutt. 2007, OLTP I/O Traces. Available: http://traces.cs.umass.edu/index.php/storage/storage
[3] S. Boboila and P. Desnoyers, "Write Endurance in Flash Drives: Measurements and Analysis," in FAST '10: Proceedings of the Conference on File and Storage Technologies, 2010.
[4] M. Cao, T. Tso, B. Pulavarty, S. Bhattacharya, A. Dilger, and A. Tomas, "State of the art: Where we are with the ext3 filesystem," in Ottawa Linux Symposium, 2005.
[5] L.-P. Chang, "Hybrid solid-state disks: combining heterogeneous NAND flash in large SSDs," in ASP-DAC {'}08: Proceedings of the 2008 Asia and South Pacific Design Automation Conference, Los Alamitos, CA, USA, 2008, pp. 428-433.
[6] A. Gupta, Y. Kim, and B. Urgaonkar, "DFTL: a flash translation layer employing demand-based selective caching of page-level address mappings," in ASPLOS {'}09: Proceeding of the 14th international conference on Architectural support for programming languages and operating systems, New York, NY, USA, 2009, pp. 229-240.
[7] Y. Hu, H. Jiang, D. Feng, L. Tian, S. Zhang, J. Liu, W. Tong, Y. Qin, and L. Wang, "Achieving page-mapping FTL performance at block-mapping FTL cost by hiding address translation," in Mass Storage Systems and Technologies (MSST), 2010 IEEE 26th Symposium on, 2010, pp. 1-12.
[8] L. Hyun-Seob, Y. Hyun-Sik, and L. Dong-Ho, "HFTL: hybrid flash translation layer based on hot data identification for flash memory," Consumer Electronics, IEEE Transactions on, vol. 55, pp. 2005-2011, 2009.
[9] C. Hyunjin, S. Dongkun, and E. Young Ik, "KAST: K-associative sector translation for NAND flash memory in real-time systems," in Design, Automation & Test in Europe Conference & Exhibition, 2009. DATE '09., 2009, pp. 507-512.
[10] J. Katcher, "PostMark: a new file system benchmark," ed: Technical Report TR3022, Network Appliance, 1997. www. netapp. com/tech_library/3022. html, 1997.
[11] J. Kim, J. M. Kim, S. H. Noh, S. L. Min, and Y. Cho, "A space-efficient Flash translation layer for CompactFlash systems," IEEE Transactions on Consumer Electronics, vol. 48, pp. 366-375, 2002.
[12] S.-W. Lee, D.-J. Park, T.-S. Chung, D.-H. Lee, S. Park, and H.-J. Song, "A log buffer-based flash translation layer using fully-associative sector translation," ACM Trans. Embed. Comput. Syst., vol. 6, p. 18, 2007.
[13] S. Lee, D. Shin, Y.-J. Kim, and J. Kim, "LAST: locality-aware sector translation for NAND flash memory-based storage systems," SIGOPS Oper. Syst. Rev., vol. 42, pp. 36-42, 2008.
[14] S. P. Lim, S. W. Lee, and B. Moon, "FASTer FTL for Enterprise-Class Flash Memory SSDs," Storage Network Architecture and Parallel I/Os, 2010. SNAPI '10. 6th IEEE International Workshop on, 2009.
[15] R. McDougall, J. Crase, and S. Debnath, "FileBench: File System Benchmark," 2009.
[16] B.-W. Nam, G.-J. Na, and S.-W. Lee, "A Hybrid Flash Memory SSD Scheme for Enterprise Database Applications," in Web Conference (APWEB), 2010 12th International Asia-Pacific, 2010, pp. 39-44.
[17] Samsung. 2005, K9K4G08U0M Datasheet 512M x 8 Bit / 256M x 16 Bit NAND Flash Memory. Available: http://www.datasheetcatalog.com/datasheets_pdf/K/9/K/4/K9K4G08U0M.shtml