Advanced Operating Systems File System Internals 9 UNIX

Advanced Operating Systems File System Internals 9

UNIX File System Organisation • The Traditional UNIX organisation from Ed 7 onwards has been – Boot Block, Super Block, Inodes, Data 10

UNIX File System Organisation • Searching and allocation is done through logical device and inumber 11

UNIX File System Organisation • Problems of Traditional UNIX FS – Fragmentation of disc – No way to use disc geometry – Short file names 12

Berkeley Fast File System • Restructured File System organisation using cylinder groups – 1 or more cylinders per group – Identical superblocks in cylinder group – Superblocks offset for each in cylinder group 13

Berkeley Fast File System • Inode/file allocation – File inode is allocated in parent directory cylinder group – New directory placed in new cylinder group – Large and small files are segregated – Use of 8 k byte blocks & 1 k fragements 14

Berkeley Fast File System • Filename size changes – 255 character file names • Changed directory organisation – Quota system introduced – Symbolic links introduced – File truncation introduced 15

Linux file system • Added VFS – Virtual File System – Allows other system to be added – Clean, object orientated, design of system • 3 parts – Inode object – File system object 16

Virtual File System 17

Virtual File System • VFS Objects define an action for each file system • Each object has a pointer into a table of functions for each file system implementation • File system object is the hierarchy • Files found through fs-inode paring 18