Diff for "DiskStructures"

Differences between revisions 2 and 3

Root File System
Mounted File Systems
Boot Block or Sector
SuperBlock
- Static parameters of the file system: FS size, Block and fragment sizes parameters affecting allocation policies
- Problems with allocating Free blocks using the free stack.
4.2BSD changes to improve efficiency and robustness.
- Cylinder groups
- Cylinder header information: (superblock, cylinder block, and the inodes)
- Allocation issues in Cylinder Groups
- Global and Local allocation routines.

Disk Structures

We always have a root file system / and mounted files systems have a bit set in the inode indicating that they are mounted file systems. The inode has a device number which is looked up in the mount table.

Every file system is a seperate system resource. The first logical sector contains a boot block (sector) containing a bootstrap program.

The Superblock contains static parameters of the file system including:

Size of hte file system
The block and fragment sizes of data
The free blocks list (like a stack, but maintained as a linked list orginally)

Free blocks are removed and pushed from the front of the free blocks list. This allocation operation causes a files to become more and more fragmented as disk activity continues. As a result BSD 7 used only 3% of the bandwidth available to the disk drive on average.

Changes in 4.2 BSD File allocation routines

To improve efficiency and robustness, cylinder groups where born.

Back to ComputerTerms FileSystem

-  ⇤ ← Revision 2 as of 2004-03-31 19:47:57 → 
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  Editor: yakko
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+   ← Revision 3 as of 2004-03-31 19:51:20 → ⇥
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  Editor: yakko
  Comment:
-Deletions are marked like this.
+Additions are marked like this.
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-   * The free blocks list (originally a stack)
+   * The free blocks list (like a stack, but maintained as a linked list orginally)
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-Free blocks are removed and pushed from the front of the free blocks list. '''''This allocation operation causes a file system to become more and more fragmented as disk activity continues'''''.
+Free blocks are removed and pushed from the front of the free blocks list. '''''This allocation operation causes a files to become more and more fragmented as disk activity continues'''''. As a result BSD 7 used only 3% of the bandwidth available to the disk drive on average.

== Changes in 4.2 BSD File allocation routines ==

'''To improve efficiency and robustness, ''cylinder groups'' where born'''.