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File Systems File Structure 2017, Spring Pusan National University Joon-Seok Kim 1 File A collection of information Where is the file that I am looking for? System A way of organizing something which follows a set of rules #2 #3 Aisles New File #4 Blocks #1 #2 #3 #4 #5 #6 #1 PNU STEM File From user’s point of view From user process’s point of view A named, persistent collection of data A sequence of bytes of arbitrary length From operating system’s point of view A collection of disk blocks 5 PNU STEM Logical File Structure Flat file of bytes Fixed-length records Variable-length records 6 PNU STEM File System Levels User processes File system interface (system calls) Device driver interface File system implementation I/O system implementation Hardware interface Disk hardware 8 PNU STEM What is a File System? File system A way of organizing and storing files on any storage device such as a hard disk drive, solid-state drive A collection of files, blocks, directories, and file descriptors, all on one logical disk Partition Each storage device has one or more partitions, and each partition is formatted with a file system. The formatting process simply creates an empty file system of that type on the device. 9 PNU STEM Types of File Systems Disk file systems Distributed file systems Special file systems 10 PNU STEM Examples of Disk File System Operating system Default file systems Unix Unix File System (UFS1, UFS2) MINIX MINIX File System Linux Extended File System (ext2, ext3, ext4) Extents File System (XFS) Mac OS Hierarchical File System (HFS, HFS+) MS-DOS File Allocation Table (FAT12, FAT16, FAT32) Windows New Technology File System (NTFS) 11 Boot block File system descriptor File descriptors 0-7 File descriptors 8-15 File descriptors 16-23 ... PNU reserved block STEM Layout of a File System block number 0 1 2 3 … Data blocks 12 PNU STEM File System Descriptor Called superblock in UNIX Contents of the file system descriptor The total size of file system The size of the file descriptor area The first block on the free block list The location of the file descriptor of the root directory The time the file system was created, last modified, and last used Other file system meta-data 13 PNU STEM File Descriptors Called inode (index node) in UNIX Data structure that records all the meta-information about the file Maintained by the file system Separate from file itself Usually attached or connected to the file Some information visible to user/application Dates, permissions, type, name, etc. Some information primarily for OS Location on disk, locks, cached attributes 14