Chapter 10: File Systems and Storage PDF

# Chapter 10: File Systems and Storage ## File Concept - Contiguous logical address space - Types: - Data - numeric - character - binary - Program ## File Attributes - Name - only information kept in human-readable form - Identifier - unique tag (number) identifies...

# Chapter 10: File Systems and Storage ## File Concept - Contiguous logical address space - Types: - Data - numeric - character - binary - Program ## File Attributes - Name - only information kept in human-readable form - Identifier - unique tag (number) identifies file within file system - Type - needed for systems that support different types - Location - pointer to file location on device - Size - current file size - Protection - controls who can do reading, writing, executing - Time, date, and user identification - data for protection, security, and usage monitoring - Information about files are kept in the directory structure, which is maintained on the disk ## File Operations - File is an abstract data type - Create - Write - Read - Reposition within file - Delete ## File Types - Name, Extension | File Type | Usual Extension | Function | |---|---|---| | Executable | exe, com, bin or none | Ready-to-run machine-language program | | Object | obj, o | Compiled, machine language, not linked | | Source Code | c, cc, java, pas, asm, a | Source code in various languages | | Batch | bat, sh | Commands to the command interpreter | | Text | txt, doc | Textual data, documents | | Word Processor | wp, tex, rtf, doc | Various word processor formats | | Library | lib, a, so, dil | Libraries of routines for programmers | | Print or View | ps, pdf, jpg | ASCII or binary file in a format for printing or viewing | | Archive | arc, zip, tar | Related files grouped into one file, sometimes compressed, for archiving or storage | | Multimedia | mpeg, mov, rm, mp3, avi | Binary file containing audio or A/V information | ## Access Methods - Sequential Access - read next - write next - reset - Direct Access - read _n_ - write _n_ _n_ = relative block number ## Sequential-access File A horizontal bar with current position, beginning, and end labels. An arrow pointing left labeled "rewind" with another arrow labeled "read or write" going right. ## Example of Index and Relative Files - A table with a column labeled "last name" and another labeled "logical record number." - Names in the table: Adams, Arthur, Asher, Smith - A blue rectangle labeled "Smith, John social-security age" with an arrow pointing to the right. The table is labeled "index file" and the rectangle is labeled "relative file." ## Directory Structure - A collection of nodes containing information about all files - A cloud shape labeled "Directory" with four circles inside and lines drawn down from the cloud to four squares labeled "Files" : F1, F2, F3, Fn _Both the directory structure and the files reside on disk_ ## Disk Structure - Disk can be subdivided into partitions - Disks or partitions can be RAID protected against failure. - Disk or partition can be used raw - without a file system, or formatted with a file system. - Partitions also known as minidisks, slices - Entity containing file system known as a volume - Each volume containing file system also tracks that file system's info in device directory or volume table of contents. - As well as general-purpose file systems there are many special-purpose file systems, frequently all within the same operating system or computer. ## A Typical File-system Organization - A vertical rectangle divided into three sections. The top and bottom sections have "directory" and "files" labels with "partition A" and "partition B" labels outside the rectangle. - A blue rectangle to the right of the first rectangle divided into two sections with "partition C" and "files" labels. An arrow connecting the rectangles labeled "disk 1." - A second blue rectangle is to the right of the first, labeled "disk 2." - A third blue rectangle is to the right of the second, labeled "disk 3." ## Operations Performed on Directory - Search for a file - Create a file - Delete a file - List a directory - Rename a file - Traverse the file system ## Single-Level Directory - A single directory for all users - A rectangle labeled "directory" with lines drawn down to circles labeled: cat, bo, a, test, data, mail, cont, hex, records - The circles are labeled "files." - The text: "Naming problem" and "Grouping problem" are below the circles. ## Two-Level Directory - Separate directory for each user - A rectangle labeled "master file directory" with lines drawn down to 4 rectangles labeled: "user 1," "user 2," "user 3," "user 4." - Lines drawn down from these rectangles to circles labeled: cat, bo, a, test, a, data, a, test, X, data, a - The circles are labeled "files" - Text is below the circles: "Path name," "Can have the same file name for different user," "Efficient searching," "No grouping capability" ## Tree-Structured Directories - A tree structure with "root" at the top. - Branches and leaves labeled: spell, bin, programs, stat, mail, dist, find, count, hex, reorder, P, e, mail, prog, copy, prt, exp, reorder, list, find hex, count. - Circles at the end of all the branches. - Leaves at the bottom: list, obj, spell, all, last, first. ## Tree–Structured Directories (Cont) - Efficient searching - Grouping Capability - Current directory (working directory) - _cd /spell/mail/prog_ - _type list_ ## Tree–Structured Directories (Cont) - Absolute or relative path name - Creating a new file is done in current directory - Delete a file - _rm <file-name>_ - Creating a new subdirectory is done in current directory - _mkdir <dir-name>_ - Example: if in current directory _/mail_ - _mkdir count_ - A tree structure with labels: mail, prog, copy, prt, exp, count. - "Deleting "mail" ≈ deleting the entire subtree rooted by "mail." ## Access Lists and Groups - Mode of access : read, write, execute - Three classes of users: - a) owner access 7 → RWX 111 - b) group access 6 → RWX 110 - c) public access 1 → RWX 001 - Ask manager to create a group (unique name), say G, and add some users to the group. - For a particular file (say game) or subdirectory, define an appropriate access. - A table with labels: owner, group, public. Beneath the table is: "chmod 761 game" then "Attach a group to a file" then "chgrp G game" ## Windows XP Access-control List Management - A screen shot of the Windows XP Access-control List Management. ## A Sample UNIX Directory Listing | | | | | | | |---|---|---|---|---|---| | -rw-rw-r-- | 1 pbg staff | 31200 | Sep 3 08:30 | intro.ps | | | drwx------ | 5 pbg staff | 512 | Jul 8 09:33 | private/ | | | drwxrwxr-x | 2 pbg staff | 512 | Jul 8 09:35 | doc/ | | | drwxrwx--- | 2 pbg student | 512 | Aug 3 14:13 | student-proj/ | | | -rw-r--r-- | 1 pbg staff | 9423 | Feb 24 2003 | program.c | | | -rwxr-xr-x | 1 pbg staff | 20471 | Feb 24 2003 | program | | | drwx--x--x | 4 pbg faculty | 512 | Jul 31 10:31 | lib/ | | | drwx------ | 3 pbg staff | 1024 | Aug 29 06:52 | mail/ | | | drwxrwxrwx | 3 pbg staff | 512 | Jul 8 09:35 | test/ | | ## File-System Implementation - Boot control block contains info needed by system to boot OS from that volume - Volume control block contains volume details - Directory structure organizes the files - Per-file File Control Block (FCB) contains many details about the file ## A Typical File Control Block - A table with the labels: file permissions, file dates (create, access, write), file owner, group, ACL, file size, file data blocks or pointers to file data blocks. ## Allocation Methods - An allocation method refers to how disk blocks are allocated for files - Contiguous allocation - Linked allocation - Indexed allocation ## 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 ## Contiguous Allocation of Disk Space - A cylinder with blocks numbered 0 to 31, with a side table labeled directory: - file: count, start: 0, length: 2 - file: f, start: 14, length: 3 - file: tr, start: 19, length: 6 - file: list, start: 28, length: 4 - file: f, start: 6, length: 2 - The blocks 0-3 are labeled together "count," blocks 14-16 are labeled together "f," blocks 19-24 are labeled together "tr," blocks 28-31 are labeled together "list." ## Linked Allocation - Each file is a linked list of disk blocks: blocks may be scattered anywhere on the disk. - A rectangle with "block' and "pointer" labels. The rectangle is divided into an upper section and a lower section. ## Linked Allocation - A cylinder with blocks numbered 0 to 31 labeled with numbers. An arrow from block 26 to block 25. An arrow from block 24 to block 27 and another arrow from block 12 to block 15. - A side table labeled "directory:" - file: jeep, start: 9, end: 25 ## File-Allocation Table - A rectangle labeled "directory entry" with "test" outside the rectangle and "name" and "start block" labels inside. The start block is labeled "217." - A cylinder with numbered blocks. From block 217 is an arrow pointed to a block labeled "618." Another arrow is labeled "339" going to the left and to the right. Finally there is an arrow from block 618 to the right labeled "339." - A rectangle labeled "FAT" with its upper section labeled "no. of disk blocks" and its lower section labeled "-1." ## Indexed Allocation - Brings all pointers together into the index block - Logical view - A set of rectangles with an arrow pointing right from each to a circle. Those rectangles below are labeled "index table." ## Example of Indexed Allocation - A cylinder with blocks numbered 0-31. An arrow from the blocks 9, 1, 10, and 25 outside of the cylinder pointing to a labeled "index block" labeled "19." - A rectangle labeled "directory" with the following table: - file: jeep - index block: 19 - A circle with these numbers inside: 9, 1, 10, 25, -1, -1. ## End of Chapter 10