File Systems Guide to Operating Systems Third Edition

File Systems Guide to Operating Systems Third Edition 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 (FAT 16, FAT 32, 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 Net. Ware 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 (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: – FAT 16 – FAT 32 – NTFS version 5 Guide to Operating Systems, Third Edition 22

Extended FAT 16 • Evolved from FAT 16 system in earlier versions of Windows • Uses long file names • Uses Unicode – Coding system Guide to Operating Systems, Third Edition 23

Extended FAT 16 (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 FAT 16 (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 FAT 16 (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 FAT 16 (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 FAT 16 (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 FAT 16 (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

FAT 32 • Accommodates larger disks than FAT 16 • Allows partitions of up to 2 TB • Windows 2000, XP, Server 2003 – convert from FAT 16 or FAT 32 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 C 2 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/ext 2/ext 3) 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 Net. Ware 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 Net. Ware 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 Net. Ware 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 Simple. Text 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) • Mac. Binary – joins the two forks into one, and safely stores the type and creator codes and finder flags • Bin. Hex – 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 • FAT 32 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