中科大操作系统原理与实现课件11_FS Implementation2.pdf

.操作系统原理与设计第11章文件系统的实现2陈香兰中国科学技术大学计算机学院2009年09月01日.提纲Efficiency and PerformanceRecoveryLog Structured File Systems小结和作业.EfficiencyIEfficiency dependent on:Idisk allocation and directory algorithmsIVarious approachesIInodes distributionIVariable cluster sizeITypes of data kept in files directory entryILarge pointers provides larger file length,but cost more diskspace.PerformanceIPerformanceIdisk cache separate section of main memory for frequentlyused blocksIfree-behind and read-ahead techniques to optimizesequential accessIimprove PC performance by dedicating section of memory asvirtual disk,or RAM disk.Page Cache IIA page cache caches pages rather than disk blocks usingvirtual memory techniquesIMemory-mapped I/O uses a page cacheIRoutine I/O through the file system uses the buffer(disk)cacheIThis leads to the following figureII/O Without a Unified Buffer Cache.Page Cache II.Unified Buffer CacheIA unified buffer cache uses the same page cache to cacheboth memory-mapped pages and ordinary file system I/OII/O Using a Unified Buffer Cache.RecoveryIConsistency checkingIcompares data in directory structure with data blocks on disk,and tries to fix inconsistenciesIBackup&restoreIUse system programs to back up data from disk to anotherstorage device(floppy disk,magnetic tape,other magneticdisk,optical)IRecover lost file or disk by restoring data from backup.Log Structured File SystemsILog structured(or journaling)file systems record eachupdate to the file system as a transactionIAll transactions are written to a logIA transaction is considered committed once it is written to thelogIHowever,the file system may not yet be updatedIThe transactions in the log are asynchronously written to thefile systemIWhen the file system is modified,the transaction is removedfrom the logIIf the file system crashes,all remaining transactions in the logmust still be performed.小结Efficiency and PerformanceRecoveryLog Structured File Systems小结和作业.作业I华夏班：11.6I非华夏班：12.6.谢谢！