软件操作系统教学（ANDREW S. TANENBAUM）MOS-3e-04.pptVIP

Backups to tape are generally made to handle one of two potential problems: Recover from disaster. Recover from stupidity. File System Backups (1) Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Figure 4-25. A file system to be dumped. Squares are directories, circles are files. Shaded items have been modified since last dump. Each directory and file is labeled by its i-node number. File System Backups (2) Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 MODERN OPERATING SYSTEMSThird EditionANDREW S. TANENBAUMChapter 4File Systems Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Essential requirements for long-term information storage: It must be possible to store a very large amount of information. The information must survive the termination of the process using it. Multiple processes must be able to access the information concurrently. File Systems (1) Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Think of a disk as a linear sequence of fixed-size blocks and supporting reading and writing of blocks. Questions that quickly arise: How do you find information? How do you keep one user from reading another’s data? How do you know which blocks are free? File Systems (2) Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Figure 4-1. Some typical file extensions. File Naming Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Figure 4-2. Three kinds of files. (a) Byte sequence. (b) Record sequence. (c) Tree. File Structure Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved. 0-13-6006639 Figure 4