lec32 - LECTURE - 32 Lecture Outline Log-Structured File...

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Unformatted text preview: LECTURE - 32 Lecture Outline Log-Structured File System (LFS) [RO91] RAID Scribe for today? Log-Structured File System Technological under-pinnings: Disk I/O becoming bottleneck since CPUs are getting faster Disk I/O dominated by writes, since reads mostly served by main memory caching Characteristics of application workloads: Lots of accesses to small files Random disk I/Os Synchronous meta-data update in FFS => slow FFS could use only about 5% disk bandwidth The Log as the Structure Large asynchronous writes (0.5-1MB) to the end of the log How to retrieve information from the log? Sequential search would be too slow I-node structure is same as in FFS Getting to i-node given the i-node number uses i-node map (level of indirection) I-node map is small enough to be in memory Free Space Management What if log fills up disk? Threading vs. copying Intermediate solution: segments Thread across segments Copy within segments Segment cleaning: copy live-data out of segment, to create free segments Segment with long-lived copy ==> can ignore while cleaning Segment Cleaning...
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lec32 - LECTURE - 32 Lecture Outline Log-Structured File...

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