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January 11, 2012 File Systems File Systems Lecture Notes for CS 140 Winter 2012 John Ousterhout Readings for this topic from Operating System Concepts : Sections 10.1-10.2, Sections 11.1- 11.2, Sections 11.4-11.6, Section 12.4. Problems addressed by modern file systems: Disk Management: Fast access to files (minimize seeks) Sharing space between users Efficient use of disk space Naming: how do users select files? Protection: isolation between users, controlled sharing. Reliability: information must last safely for long periods of time. File: a named collection of bytes stored on durable storage such as disk. File access patterns: Sequential: information is processed in order, one byte after another. Random Access: can address any byte in the file directly without passing through its predecessors. E.g. the data set for demand paging, also databases. Keyed: search for blocks with particular values, e.g. hash table, associative database, dictionary. Usually provided by databases, not operating system. File Descriptors How should disk sectors be used to represent the bytes of a file? File descriptor : Data structure that describes a file; stored on disk along with file data. Info in file descriptor: Sectors occupied by file File size Access times (last read, last write) Protection information (owner id, group id, etc.) Issues to consider: Most files are small (a few kilobytes or less). Most of the disk space is in large files. Many of the I/O operations are for large files.
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This note was uploaded on 04/02/2012 for the course CS 140 taught by Professor Rosenblum during the Winter '08 term at Stanford.

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v13stanford.edu-File_Systems - File Systems http:/w w w

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