Disk Scrubbing in Large Archival Storage Systems大型档案存储系统中的磁盘清理.pptVIP

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Disk Scrubbing in Large Archival Storage Systems大型档案存储系统中的磁盘清理.ppt

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Disk Scrubbing in Large Archival Storage Systems Thomas Schwarz, S.J.1,2 Qin Xin1,3, Ethan Miller1, Darrell Long1, Andy Hospodor1,2, Spencer Ng3 1 Storage Systems Resource Center, U. of California, Santa Cruz 2 Santa Clara University, Santa Clara, CA 3 Hitachi Global Storage Technologies, San Jose Research Center, Introduction Large archival storage systems: Protect data more proactively Keep disks powered off for long periods of time Have low rate of data access Protect data by storing it redundantly. Introduction Failures can happen At the block level. At the device level. Failures may remain undetected for long periods of time. A failure may unmask one or more additional failures. Reconstruction procedure accesses data on other devices. Those devices can have suffered previous failures. Introduction We investigate the efficacy of disk scrubbing. Disk Scrubbing accesses a disk to see whether the data can still be read. Reading a single block shows that the device still works. Reading all blocks shows that we can read all the data on the block. Contents Disk Failure Taxonomy System Overview Disk Scrubbing Modeling Power Cycles and Reliability Optimal Scrubbing Interval Simulation Results Disk Failure Taxonomy Disk Blocks 512B sector uses error control coding Read to a block successfully either corrects all errors, or retries and then: flags block as unreadable, or misreads block. Disk Failure Rates Depend highly on Environment: Temperature, Vibrations, Air quality Age. Vintage. Disk Failure Taxonomy Block Failure Rate estimate: Since: 1/3 of all field returns for server drives are due to hard errors. RAID users (90%) do not return drives with hard errors. 10% of all disks sold account for 1/3 of all errors. Hence: Mean Time between Block Failures is 3/10 MTBF of all disk failures. Mean time to disk failure is 3/2 of MTBF. 1 million hour rated drive has 3*105 mean time between block failure. 1.5*106 mean time between disk failure. System Overview Disks are p