nlhdh_tuan9 - 1 1 Silberschatz Galvin and Gagne © 2002...

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Unformatted text preview: 1 1 Silberschatz, Galvin and Gagne © 2002 12.1 Operating System Concepts Chapter 12: File System Implementation ¡ File System Structure ¡ File System Implementation ¡ Directory Implementation ¡ Allocation Methods ¡ Free-Space Management ¡ Efficiency and Performance ¡ Recovery ¡ Log-Structured File Systems ¡ NFS Silberschatz, Galvin and Gagne © 2002 12.2 Operating System Concepts File-System Structure ¡ File structure ) Logical storage unit ) Collection of related information ¡ File system resides on secondary storage (disks). ¡ File system organized into layers. ¡ File control block – storage structure consisting of information about a file. Silberschatz, Galvin and Gagne © 2002 12.3 Operating System Concepts Layered File System Silberschatz, Galvin and Gagne © 2002 12.4 Operating System Concepts A Typical File Control Block Silberschatz, Galvin and Gagne © 2002 12.5 Operating System Concepts In-Memory File System Structures ¡ The following figure illustrates the necessary file system structures provided by the operating systems. ¡ Figure 12-3(a) refers to opening a file. ¡ Figure 12-3(b) refers to reading a file. Silberschatz, Galvin and Gagne © 2002 12.6 Operating System Concepts In-Memory File System Structures 2 2 Silberschatz, Galvin and Gagne © 2002 12.7 Operating System Concepts Virtual File Systems ¡ Virtual File Systems (VFS) provide an object-oriented way of implementing file systems. ¡ VFS allows the same system call interface (the API) to be used for different types of file systems. ¡ The API is to the VFS interface, rather than any specific type of file system. Silberschatz, Galvin and Gagne © 2002 12.8 Operating System Concepts Schematic View of Virtual File System Silberschatz, Galvin and Gagne © 2002 12.9 Operating System Concepts Directory Implementation ¡ Linear list of file names with pointer to the data blocks. ) simple to program ) time-consuming to execute ¡ Hash Table – linear list with hash data structure. ) decreases directory search time ) collisions – situations where two file names hash to the same location ) fixed size Silberschatz, Galvin and Gagne © 2002 12.10 Operating System Concepts Allocation Methods ¡ An allocation method refers to how disk blocks are allocated for files: ¡ Contiguous allocation ¡ Linked allocation ¡ Indexed allocation Silberschatz, Galvin and Gagne © 2002 12.11 Operating System Concepts Contiguous Allocation ¡ Each file occupies a set of contiguous blocks on the disk. ¡ Simple – only starting location (block #) and length (number of blocks) are required. ¡ Random access. ¡ Wasteful of space (dynamic storage-allocation problem). ¡ Files cannot grow. Silberschatz, Galvin and Gagne © 2002 12.12 Operating System Concepts Contiguous Allocation of Disk Space 3 3 Silberschatz, Galvin and Gagne © 2002 12.13 Operating System Concepts Extent-Based Systems ¡ Many newer file systems (I.e. Veritas File System) use a modified contiguous allocation scheme....
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This note was uploaded on 01/18/2012 for the course INFORMATIK 2011 taught by Professor Phanthuongcang during the Winter '11 term at Cornell.

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nlhdh_tuan9 - 1 1 Silberschatz Galvin and Gagne © 2002...

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