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Transcript
File Systems Guide to Operating Systems Third Edition Objectives After reading this chapter and completing the exercises you will be able to: • Understand the basic functions common to all file systems • Explain the design of the Windows 2000, Windows XP, and Windows Server 2003 (FAT16, FAT32, and NTFS) Guide to Operating Systems, Third Edition 2 Objectives (continued) • Describe the file systems used by UNIX and Linux systems, including ufs and ext • Discuss the NetWare file system and NSS • Explain the Mac OS X Extended (HFS+) file system including features added in Mac OS X version 10.3 Guide to Operating Systems, Third Edition 3 Understanding File System Functions • File system is designed for storing and managing files on storage media • PC file systems: – Partition and format disks to store and retrieve information – Enable files to be organized through directories and folders – Establish file-naming conventions Guide to Operating Systems, Third Edition 4 Understanding File System Functions (continued) • PC file systems (continued): – Provide utilities to maintain and manage the file system and storage media – Provide for file and data integrity – Enable error recovery or prevention – Secure the information in files Guide to Operating Systems, Third Edition 5 Understanding File System Functions (continued) • Purpose of a file system is to create a structure for filing data • A file is a set of data that is grouped in some logical manner • Data can be text, images, music and sounds, video, etc Guide to Operating Systems, Third Edition 6 Understanding File System Functions (continued) • Must be a way to write digital information onto disk, track it, update it, and recall it • OS typically groups disk sectors in some logical way, creates a record of this structure, and builds a directory to track the type of data stored in each file Guide to Operating Systems, Third Edition 7 Understanding File System Functions (continued) • Directories also store: – Date and time the directory or file was created – Date and time the directory or file was last modified – Directory or file size – Directory of file attributes Guide to Operating Systems, Third Edition 8 Designing a Directory Structure • Important feature: – ability to store information according to a pattern of organization that is enabled by the use of directories • Windows versions and the Mac OS, these are called folders Guide to Operating Systems, Third Edition 9 Designing a Directory Structure (continued) • Directories and folders – can be organized in a hierarchy that is similar to a tree structure • Many keep most of their files in the computer’s primary level or root directory Guide to Operating Systems, Third Edition 10 Designing a Directory Structure (continued) • Consider directories for the following: – Operating system files – Software applications – Work files, such as word processing, graphics, spreadsheets, and database files – Public files that you share over the network – Utilities files – Temporary files Guide to Operating Systems, Third Edition 11 Designing a Directory Structure (continued) • The folder structure from the root might be as follows: – Windows – Program Files Documents and Settings – Shared – Forms – Inetpub Guide to Operating Systems, Third Edition 12 Designing a Directory Structure (continued) • For UNIX/Linux systems: – bin – lib – usr – var – tmp Guide to Operating Systems, Third Edition 13 Designing a Directory Structure (continued) • For UNIX/Linux systems (continued): – dev – mnt – etc – sbin – home – proc Guide to Operating Systems, Third Edition 14 Designing a Directory Structure (continued) • In Mac OS X: – Applications – Applications (Mac OS 9) – System Folder Library – System Guide to Operating Systems, Third Edition 15 Designing a Directory Structure (continued) • In Mac OS X (continued): – Library – Users – Documents Guide to Operating Systems, Third Edition 16 Disk Storage Basics • Low-level format – software process that marks the location of disk tracks and sectors Guide to Operating Systems, Third Edition 17 Block Allocation • Block allocation – keep track of where specific files are stored on the disk • Clusters – Logical blocks mapped to sectors, heads, and tracks on the disk Guide to Operating Systems, Third Edition 18 Block Allocation (continued) • Block allocation information is stored: – FAT (file allocation table) – New Technology File System (NTFS) Guide to Operating Systems, Third Edition 19 Partitions • Partitioning – process of blocking a group of tracks and sectors to be used FAT or NTFS • High-level formatted – disk divisions and patterns needed by a particular operating system to store files Guide to Operating Systems, Third Edition 20 Partitions (continued) • Partition table in Mac OS and Windows • Disk label in UNIX • Boot block in UNIX Master Boot Record (MBR) in Windows – tiny program used to begin booting an operating system from a disk Guide to Operating Systems, Third Edition 21 Windows 2000/XP/Server 2003 File Systems • Three file systems supported: – FAT16 – FAT32 – NTFS version 5 Guide to Operating Systems, Third Edition 22 Extended FAT16 • Evolved from FAT16 system in earlier versions of Windows • Uses long file names • Uses Unicode – Coding system Guide to Operating Systems, Third Edition 23 Extended FAT16 (continued) • Assigned a letter followed by a colon: A:, B:, C:, and so on through Z: • Typically, C: is reserved for the first hard disk Guide to Operating Systems, Third Edition 24 Extended FAT16 (continued) • Format command – writes the file system structure to the disk – includes several additional switches that modify precise program operation Guide to Operating Systems, Third Edition 25 Extended FAT16 (continued) • Switches – (extra code) to change the way a particular command operates • File attributes – file characteristics such a Hidden, Read-only, Archive, etc. Guide to Operating Systems, Third Edition 26 Extended FAT16 (continued) • File stored to disk – data is written in the clusters on the disk – Filename stored in the directory Guide to Operating Systems, Third Edition 27 Extended FAT16 (continued) • “linked-list” method • Bad clusters – areas never used for file storage • Formatting a disk – removes all data that was on the disk • The FAT tables and root directory are found at the beginning • Each item in a directory consists of 32 bytes Guide to Operating Systems, Third Edition 28 Extended FAT16 (continued) • Status bits – identify the type of filename contained in each entry – Volume, Directory, System, Hidden, Read-only, and Archive • attrib command – to look at or set attributes – typing attrib in a directory shows all settings Guide to Operating Systems, Third Edition 29 FAT32 • Accommodates larger disks than FAT16 • Allows partitions of up to 2 TB • Windows 2000, XP, Server 2003 – convert from FAT16 or FAT32 to NTFS Guide to Operating Systems, Third Edition 30 NTFS • Advantages of NTFS: – Ability to compress file and directory contents on the fly – Better recoverability and stability – Less disk fragmentation – Local file and folder-level security Guide to Operating Systems, Third Edition 31 NTFS (continued) • Basic features: – Long filenames (LFN) – Built-in security features – Better file compression than FAT – Ability to use larger disks and files Guide to Operating Systems, Third Edition 32 NTFS (continued) • Basic features: – File activity tracking for better recovery and stability than FAT – POSIX support – Volume striping and volume extensions – Less disk fragmentation than FAT Guide to Operating Systems, Third Edition 33 NTFS (continued) • Enables the use of LFNs • Equipped with security features that meet the U.S. government’s C2 security specifications – high-level, “top secret” standards for data protection, system auditing, and system access Guide to Operating Systems, Third Edition 34 NTFS (continued) • Large databases – SQL Server database file might be 20 GB • Ability to keep a log of file system activity • Supports POSIX to enable portability of applications Guide to Operating Systems, Third Edition 35 NTFS (continued) • NTFS 5 adds several new features: – Ability to encrypt files – No system reboot required after creating an extended volume – Ability to reduce drive designations – Indexing for fast access – Ability to retain shortcuts and other file information – Ability to establish disk quotas Guide to Operating Systems, Third Edition 36 NTFS (continued) • NTFS 5 files can be encrypted • Distributed Link Tracking – available in NTFS 5 so that shortcuts are not lost when you move files to another volume • Uses a Master File Table (MFT) – located at the beginning of the partition – when a file is made in NTFS, a record for that file is added to the MFT Guide to Operating Systems, Third Edition 37 NTFS (continued) • Basic disks – use traditional disk management • Dynamic disks – setup large volumes on one disk – extend volumes onto additional physical disks • chkdsk utility – much more robust than in other Windows operating systems Guide to Operating Systems, Third Edition 38 NTFS (continued) • CD-ROM File System (CDFS) – OS can read and write files to CD-ROM • Universal Disk Format (UDF) – used on CD-ROM and large capacity Digital Video Disk-Read Only Memory (DVD-ROM) media Guide to Operating Systems, Third Edition 39 The UNIX File System • Works differently from anything discussed up to this point • “UNIX file system” is really a misnomer – many different file systems that can be used • Extended file system (ext or ext fs) – native in Linux and installed by default – ufs UNIX file system (and also ext/ext2/ext3) uses the concept of information nodes, or inodes Guide to Operating Systems, Third Edition 40 The UNIX File System (continued) • An inode contains – name of file – general information about the file – information (pointer) • Pointer information based on logical blocks • Superblock – information about the layout of blocks, sectors, and cylinder groups Guide to Operating Systems, Third Edition 41 The UNIX File System (continued) • mount command – OS told to map the root inode of another file system onto the empty directory • Directory is nothing more than a special file • Two types of devices – raw devices and block devices – Raw device has no logical division in blocks, whereas a block device does Guide to Operating Systems, Third Edition 42 The UNIX File System (continued) • Every device must be represented by a device inode • Symbolic link – to link a directory entry to a file that is on a different partition Guide to Operating Systems, Third Edition 43 The NetWare File System • Novell Storage Services (NSS) – disk partitions – storage pools – volumes • Storage pools – ways to divide the use of a disk – can be a superset of disk partitions Guide to Operating Systems, Third Edition 44 The NetWare File System (continued) • Balanced-tree (b-tree) – fast file access – tree structure off the root • Features of NSS – file compression – hot fixes – journaling – user disk quotas Guide to Operating Systems, Third Edition 45 The NetWare File System (continued) • Features of NSS – file flushing – storage pool expansion – data shredding – improved file backup Guide to Operating Systems, Third Edition 46 The Macintosh File System • Macintosh Filing System (MFS) – limited to keeping track of 128 documents, applications, or folders • Hierarchical Filing System (HFS) – at most, 216 (65,536) units Guide to Operating Systems, Third Edition 47 The Macintosh File System (continued) • Boot blocks – identify the filing system, the names of important system files, and other important information • Volume information block – points to other important areas of information Guide to Operating Systems, Third Edition 48 The Macintosh File System (continued) • Catalog b-tree – list of all files on the volume • Extents b-tree – track the location of the file fragments, or extents • “medium” filenames – up to 31 characters in length Guide to Operating Systems, Third Edition 49 The Macintosh File System (continued) • Invisible type codes and creator codes • Files created with Apple’s SimpleText text editor have a type code of TEXT, and a creator code of ttxt • Mac files an contain two parts, or forks: – the data fork – the resource fork Guide to Operating Systems, Third Edition 50 The Macintosh File System (continued) • Data fork – frequently changing information (such as word processing data) • Resource fork – information that is fixed Guide to Operating Systems, Third Edition 51 The Macintosh File System (continued) • MacBinary – joins the two forks into one, and safely stores the type and creator codes and finder flags • BinHex – transforms all files into seven-bit files using the ASCII character set Guide to Operating Systems, Third Edition 52 The Macintosh File System (continued) • Alias – Apple’s equivalent of the UNIX link and Windows shortcut – Files, folders, applications, and disks can be aliased Guide to Operating Systems, Third Edition 53 The Macintosh File System (continued) • Two basic disk utilities: – Disk First Aid and Disk Utility • Sherlock – search disks for filenames and text within files Guide to Operating Systems, Third Edition 54 Summary • Files are the “bread and butter” of an operating system • Files hold documents and programs on which users rely • File allocation table (FAT) file system creates a file allocation table to store information about files Guide to Operating Systems, Third Edition 55 Summary (continued) • The fdisk and format utilities are used with all versions of FAT file systems to partition and format disks • FAT32 file system was introduced in the second release of Windows 95 Guide to Operating Systems, Third Edition 56 Summary (continued) • The native file system for Windows NT, 2000, XP, and Server 2003 is called NTFS • NTFS is a more stable and secure file system than FAT • UNIX file systems use information nodes (inodes) to organize information about files Guide to Operating Systems, Third Edition 57 Summary (continued) • A UNIX system can have many file systems mounted as subdirectories of the root • The Macintosh OS uses the Hierarchical Filing System (HFS) Guide to Operating Systems, Third Edition 58