【作者】 陈华；

【导师】 杜旭；

【作者基本信息】 华中科技大学 ， 通信与信息系统， 2013， 硕士

【摘要】 随着技术的发展，音视频相关的应用逐渐普及，类似行车记录仪的便携式多媒体存储系统更多的深入人们的生活。便携式嵌入式设备多使用SD卡、U盘等可移动存储设备，以方便与PC机交换数据。由于FAT文件系统在各个操作系统上良好的兼容性，目前大多数便携式嵌入式设备均使用FAT文件系统来存储数据。但是，FAT文件系统在进行音视频多媒体存储特别是多路并发存储时，会产生严重的碎片，影响读写性能。多媒体文件通常具有很大数据量，容易形成文件碎片。在并发存储情况下，顺序查找空闲簇并分配的策略使得不同文件的数据簇交织存储，恶化了文件碎片情况。FAT文件系统的另一不足是对FAT表的严重依赖，文件的读写过程中对FAT表频繁访问的IO开销一定程度上影响了读写效率。多媒体文件存储与传统文本存储不同，它具有一次写入多次读取，顺序访问，大数据量等特点，而FAT文件系统作为一种通用文件系统并不能很好地适应这些特点。本文将结合多媒体文件的存储特性，在保持兼容性的前提下对FAT文件系统进行改进，使之更适合多媒体的存储。改进工作包含两个方面，一方面是在内存中建立FAT表的位图索引完成空闲簇的搜索，以便减少系统IO负荷；另一方面是在位图索引基础上，提出一种基于簇组的可变大小块分配机制，用于扩展空闲块分配单元大小。论文通过测试表明，以上改进提升了FAT文件系统在多路并发存储条件下对于大文件的读写性能。更多还原

【Abstract】 With the development of technology, audio and video related applications arebecoming more common, portable multimedia storage system like vehicle recorderbecomes more and more important in people’s life. In order to exchange data with PC,embedded devices usually use SD cards, U disks or other removable storage devices.Because of the excellent compatibility of FAT file system in various operating systems,most portable embedded devices use it as their file system.However, the FAT file system will cause severe fragmentation when used to storemultimedia files, especially in concurrent storage environment, affecting read and writeperformance. In concurrency storage case, free cluster allocation strategy makes the dataclusters of different multimedia files interleaving, deteriorating file fragmentation.Another deficiency of FAT file system is its heavily dependence on FAT table, the IO offrequently accessing to FAT affects read-write efficiency.Multimedia files are usually written once but read many times, accessed in sequenceand of a large amount of data. However, the FAT file system as a general-purpose filesystem is not well adapted to these characteristics. In this thesis, some improvements aremade to make FAT file system more suitable for multimedia storage. Firstly, bitmapindex is established in memory for FAT table to accelerate the search of free clusters.Secondly, a variable size block allocation mechanism based on the cluster group isintroduced for the expansion of the free block allocation unit size. Tests show aboveimprovements can enhance read and write performance of the FAT file system for theconcurrent storage of large files.更多还原