Unix File System - Design

Design

A UFS volume is composed of the following parts:

  • a few blocks at the beginning of the partition reserved for boot blocks (which must be initialized separately from the filesystem)
  • a superblock, containing a magic number identifying this as a UFS filesystem, and some other vital numbers describing this filesystem's geometry and statistics and behavioral tuning parameters
  • a collection of cylinder groups. Each cylinder group has the following components:
    • a backup copy of the superblock
    • a cylinder group header, with statistics, free lists, etc., about this cylinder group, similar to those in the superblock
    • a number of inodes, each containing file attributes
    • a number of data blocks

Inodes are numbered sequentially, starting at 0. The first two inodes are reserved for historical reasons, followed by the inode for the root directory, which is always inode 2.

Directory files contain only the list of filenames in the directory and the inode associated with each file. All file metadata is kept in the inode.

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