Research Of Flash FTL Algorithm Based On Security USB Disk

USB disk is a micro-high-capacity mobile storage device without physical drives,due to it's portable,fast operation,storage capacity and anti-magnetic properties,it has become one of the indispensable storage devices in people's life.USB disk uses flash memory as a storage medium,thus the file system can't be accessed directly from the USB disk,there are Flash Translation Layer(FTL)between file system and flash memory chip.As one of the Key technologies in USB disk storage system,FTL algorithm acts very important roles in product performance and reliability.In addition,people pay more attention on security problem of the data stored in the USB disk,a FTL algorithm based on three-level address mapping is designed with a secure USB flash controller by Hangzhou Sage Microelectronics Corp.The article first introduced security USB disk structure and the USB flash controller chip S261,and according to the characteristics of S261 chip,the data security function of USB disk is analyzed.Several FTL algorithms with high utilization rate are analyzed in detail,the FTL algorithm is proposed in this paper on the basis of their and combined with the actual USB disk parameters.The FTL algorithm designed in this paper is a hybrid FTL algorithm,it includes three levels of address mapping architecture,block management system,garbage collection system and power-down recovery system four modules,and complete the preparation of the algorithm code in the firmware.Three level address mapping strategy mainly through CIT,PIT and SIT mapping table to achieve the three host addressing,and proposes an optimized addressing strategy based on it,which improves the efficiency of addressing.Block management system proposed EMBT,ERBT two empty block table and BBT concept,it ensure that the program and erase endurance performance of flash memory is balanced,effective management of the bad block in flash memory and extend flash memory life.The garbage collection system proposes the concept of full merge and partial merge,it recover physical blocks which has small numbers of VPs preferentially,thereby improving the block recovery efficiency.Power-down recovery system is used to achieve the case of power-down in the system to accurately restore the PIT and SIT,to ensure the data reliability of the entire USB disk.Finally,the algorithm firmware is applied to security to the security U disk for testing,the results show that the proposed algorithm not only guarantees the reliability and performance.