Lecture notes for Operating Systems

Lecture Notes for Operating Systems

File Systems, 5 December 2001

File systems tie everything together
1. each file system is a consistent view of storage - protection, access, operations, metadata and so on
2. there may be (usually are) several file systems in an os
The file manager provides a uniform interface to all the file systems
storage
1. generally, a single storage device is divided into partitions
  1. each partition is a contiguous group of cylinders on a disk
  2. good for accounting (who owns what), autonomous management (separate quota or protection policies), reliability (replicated and independent metadata), performance (swap partitions)
  3. partitioning has extra overhead, can fragment access patterns, causing performance loss
2. each partition holds a file system
  1. sometimes, a file system can span partitions (aix)
  2. file-system code configures an empty partition into a file system
  3. the superblock or file-control block contains file-system information - size, directory and metadata locations, bad-sector mappings, spare sectors, boot information
  4. file systems can impose more structure on partitions - cylinder groups in bsd unix; clusters in nt; performance related
3. pasting together file systems
  1. tree-shaped hierarchies - paste the root of one file system into another file system
  2. mounting file systems
  3. this is a flexible and powerful way to build file systems
  4. it's relatively simple to do to
  5. plan 9 carries this to the extreme - per-process file systems, pasted together from bits and pieces of other file systems
4. interesting file systems
  1. remote file systems
    1. move the file system to another machine - local and remote proxies
    2. move the storage device to another machine - san or nas
  2. /proc file systems
    1. access processes as if they were files
    2. a synthetic file system
This page last modified on 5 December 2001.