ch11 (2) - Chapter 11: File System Implementation...

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Silberschatz, Galvin and Gagne ©2009 Chapter 11: File System Implementation
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11.2 Silberschatz, Galvin and Gagne ©2009 Chapter 11: 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 Example: WAFL File System
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11.3 Silberschatz, Galvin and Gagne ©2009 Objectives To describe the details of implementing local file systems and directory structures To describe the implementation of remote file systems To discuss block allocation and free-block algorithms and trade-offs
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11.4 Silberschatz, Galvin and Gagne ©2009 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
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11.5 Silberschatz, Galvin and Gagne ©2009 Layered File System
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11.6 Silberschatz, Galvin and Gagne ©2009 A Typical File Control Block
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11.7 Silberschatz, Galvin and Gagne ©2009 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.
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11.8 Silberschatz, Galvin and Gagne ©2009 In-Memory File System Structures
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11.9 Silberschatz, Galvin and Gagne ©2009 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.
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11.10 Silberschatz, Galvin and Gagne ©2009 Schematic View of Virtual File System
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11.11 Silberschatz, Galvin and Gagne ©2009 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
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11.12 Silberschatz, Galvin and Gagne ©2009 Allocation Methods An allocation method refers to how disk blocks are allocated for files: Contiguous allocation Linked allocation Indexed allocation
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11.13 Silberschatz, Galvin and Gagne ©2009 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
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11.14 Silberschatz, Galvin and Gagne ©2009 Contiguous Allocation Mapping from logical to physical LA/512 Q R Block to be accessed = ! + starting address Displacement into block = R
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11.15 Silberschatz, Galvin and Gagne ©2009 Contiguous Allocation of Disk Space
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11.16
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ch11 (2) - Chapter 11: File System Implementation...

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