lecture21 - File System Implementation - Performance This...

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File System Implementation - Performance This lecture discusses the details of making the file system perform well. This is primarily done with twomechanisms - caching and file layout. Caching Fa rand awaythe most effective strategy for improving file system performance is caching. Every time a file is opened or created it requires accesses to all the directories from the root to the file itself, and manyfiles are referenced often. Consider executables for commonly executed utilities. Accesses to the physical disk for these common cases can be avoided if the blocks that would have been read from the disk are cached in memory rather than being read from disk each time. OS 32 13 25 8 24 29 14 12 Disk 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Cached Blocks Caching is accomplished by setting aside a portion of memory and using it to store blocks as theyare brought into memory .Blocks are read or written into the memory if possible and written out to disk when convenient or when the block must be removedfrom the cache to makeway for a newblock. The important issue with anycaching system is the tradeoffbetween performance and consistencyof the caching system. In this case that means the difference between the versions of file blocks that are in the cache and on the disk. During operation this distinction isn’
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This note was uploaded on 02/28/2008 for the course CS 402 taught by Professor Tedfaber during the Spring '05 term at USC.

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lecture21 - File System Implementation - Performance This...

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