File Blocks And File Extents

• The data of files is stored in disk blocks...
  • whose identities are stored in the file's inode...
  • ...either directly, or indirectly (via indirect inode blocks)
• On some file-systems (e.g. ext2, ext3) blocks are allocated only when there is a need to write into them.
  • Pros:
    • Good disk space utilization for small files and sparse files.
  • Cons:
    • Can cause file fragmentation - making large sequential data read/write operations require many disk seeks.
    • May cause a need to use more indirect inode blocks - making random file access work much worse.

Originally written by guy keren