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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

The Original Unix File System (UFS)

• First block on disk is Boot block
  • read by firmware for booting
• Second block of disc is superblock:
  • disk geometry, incl. total number of blocks,
  • pointer to block free list.
• Next is inode array, containing pointers to disk blocks.
• Finally data blocks.

New things

• Flat files -- just a string of bytes
  • Structure imposed by user and convention
• Directories maintained by OS, just name $\Leftrightarrow$ inumber
• namei() got expensive...
• Physical volumes could be Mounted into hierarchical namespace

As discs got larger this was extended to:

• Volume table-of-contents (VTOC) at start of disk,
• Several partitions per physical disk.
• Each partition can contain a file system.
• Partitions can be mounted into hierarchical namespace.

UFS problems:

• Small block size (512b).
  • Easily fixed: Doubling doubled performance.
• No redundancy, hence easy to destroy.
  • Loss of superblock is disaster.
• No locality:
  • Inodes and data in different parts of disk.
  • Block allocation using free list leads to randomisation of file's blocks.
  • Generally no attempt to minimise rotational and seek latencies.

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