Lecture 0x16

Computer Science 432/563
Operating Systems

Spring 2016, The College of Saint Rose

Lecture 0x16: File Systems
Date: Monday, April 18, 2016

Agenda

Announcements
- Term Project, progress reports due tonight
- Lab 6: File Systems continues, due Wednesday
Lecture 0x15 assignment recap
Disks and partitions
- a system may have multiple disks, each of which contains multiple partitions
- we create a file system (more later) in each partition
- mounting: drive letters in Windows, paths in Unix
- In Unix, a virtual file system layer translates generic paths to the correct partitions (local of varying types, network-accessible)
- partitioning: why and how?
File System Implementations
- want to provide: convenience, protection, efficiency
- issues:
  - allocation of disk blocks to files/directories
  - track available blocks
  - do this efficiently
Disk block allocation methods
- contiguous allocation
- extents
- linked allocation
- variation on linked: file allocation table (FAT)
- indexed allocation
  - straightforward implementation
  - linked indexed allocation
  - two-level index
- Unix inodes
  - a combination of the best features of many of the above
  - set aside special disk blocks called inodes (index nodes)
  - inode has entries pointing to direct file blocks, a single indirect block, a double indirect block, and a triple indirect block
  - a superblock keeps track of inodes and data blocks
  - see /usr/src/sys/ufs/ufs/dinode.h in FreeBSD
- Concerns: file size limits, fragmentation, overhead, performance
Free Space Management
- bit vector
- free list
Disk cache
Journaling filesystems
Hierarchical storage
Virtual file system layer
Input/Output

Due at the start of class, Wednesday, April 20.

Please submit answers to these questions either as a hard copy (typeset or handwritten are OK) or by email to terescoj AT strose.edu by the start of class. Please use a clear subject line when submitting by email (e.g., CS 432 Lecture 0x16 Assignment, Mary Smith). We will discuss these questions at the start of class, so no late submissions are accepted.

The readings for next class are SG&G Chapter 12.

SG&G Exercise 11.9, p. 556 (6 points)
SG&G Exercise 11.11, p. 556 (4 points)
SG&G Exercise 11.13, p. 556-7 (4 points)
SG&G Exercise 11.16, p. 557 (3 points)
SG&G Exercise 11.17, p. 557 (3 points)

Links