18-File_Systems_2spp

18-File_Systems_2spp - CSE 421/521 Operating Systems Fall...

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1 CSE 421/521 - Operating Systems Fall 2011 Tevfik Ko ş ar University at Buffalo November 3 rd , 2011 Lecture - XVIII File Systems File Systems • Provides organized and efficient access to data on secondary storage: 1. Organizing data into files and directories and supporting primitives to manipulate them (create, delete, read, write etc) 2. Improve I/O efficiency between disk and memory (perform I/O in units of blocks rather than bytes) 3. Ensure confidentiality and integrity of data Contains file structure via a File Control Block (FCB) Ownership, permissions, location. .
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A Typical File Control Block Directories 4 ! Directories are special files that keep track of other files " the collection of files is systematically organized " first, disks are split into partitions that create logical volumes (can be thought of as “virtual disks”) " second, each partition contains information about the files within " this information is kept in entries in a device directory (or volume table of contents) " the directory is a symbol table that translates file names into their entries in the directory # it has a logical structure # it has an implementation structure (linked list, table, etc.)
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Directories 5 Single-level directory ! Single-level directory structure " simplest form of logical organization: one global or root directory containing all the files " problems # global namespace: unpractical in multiuser systems # no systematic organization, no groups or logical categories of files that belong together Silberschatz, A., Galvin, P. B. and Gagne. G. (2003) Operating Systems Concepts with Java (6th Edition). Directories 6 Two-level directory ! Two-level directory structure " in multiuser systems, the next step is to give each user their own private directory " avoids filename confusion " however, still no grouping: not satisfactory for users with many files Silberschatz, A., Galvin, P. B. and Gagne. G. (2003) Operating Systems Concepts with Java (6th Edition).
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18-File_Systems_2spp - CSE 421/521 Operating Systems Fall...

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