os12 - Modified from Lecture Slides for Operating System...

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Operating Systems : File System Implementation (Chapter 12) Sung-Yong Park, Ph.D. Department of Computer Science Sogang University Modified from Lecture Slides for Operating System Concepts (6 th Edition) by Silberschatz et. al. Page 2 File System Structure (1) ± File system resides on secondary storage (disks). ± For the implementation, file system has both on-disk structures and in-memory structures. ± On-disk structures ± Boot Control Block – contains information needed by the system to boot from the partition; Typically the first block of a partition; Also called boot block (UFS) or partition boot sector (NTFS) ± Partition Control Block – contains partition details, such as the # and size of blocks in partition, free block count and pointers, and free FCB (File Control Block) count, etc; Also called super-block (UFS) or master file table (NTFS). ± Directory structure ± File Control Block (FCB) – contains many of the file’s details; Also called inode (UFS).
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Page 3 File System Structure (2) ± In-memory structures – used for both file-system management and performance improvement via caching. ± In-memory partition table – contains information about each mounted partition. ± In-memory directory structure – holds the directory information of recently accessed directories. ± System-wide open-file table – contains a copy of the FCB of each open file. ± Per-process open-file table – contains a pointer to the appropriate entry in the system-wide open-file table. Page 4 In-Memory File System Structures copy locate (1) (2) search copy (3) pointer (4) file descriptor or file handle has current location (5) (6) (7) In reality, the open system call first searches the system-wide open-file table.
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Page 5 Partitions and Mounting ± A disk can be sliced into multiple partitions, or a partition can span multiple disks. ± Each partition can either be raw , containing no file system, or cooked , containing a file system. ± Raw disk can be used where no file system is appropriate; ± Swap space ± Some databases use raw disk and format the data to suit their needs. ± The root partition, which contains the OS kernel, is mounted at
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os12 - Modified from Lecture Slides for Operating System...

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