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File Systems

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File Systems File Systems Presentation Transcript

  • File Systems David Martínez
  • Content
    • Physically, what is a HD like?
    • The HD for the OS
    • Why do I need a FS?
    • FS structure in Windows
    • FS structure in Unix
    • Other FS
    • Journalling
    • Physically, what is a HD like?
    • Little exercise (Floppy)
      • 2 heads
      • 80 cylinders
      • 18 sectors
      • 512 bytes/sector
    • The HD for the OS
    • MBR – Master Boot Record
      • Bootloader
      • Partition table
    • Partitions* (limited to 4 primary)
      • File System: many, not only for HDs
      • Clusters/Blocks ( performance )
    • Driver to transform physical address to logical
    • Why do I need a FS?
    • To set a structure for the data (files, directories...)
    • Metadata (name, modification date, owner...)
    • Set a permissions system
    • Data integrity (damaged sectors)
    • Links
    • The clusters in which a file is saved (they might not be contiguous)
    • ...
    • FS structure in Windows
    • Boot Record – contains information about the different areas
    • FAT – File Allocation Table
      • One entry for each block in the data area
    Boot Record FAT Optional Duplicate FAT Data Blocks
    • The FAT family FS
    • FS structure in Unix
    • Superblock*: stores the size, number of files, free space, index of the next free inode...
    • i-node list: holds one entry for each file or directory where to save metadata, inode type, locking and modification flags...
    • Data blocks: keeps the data of the files pointed by the inodes.
    Superblock i-node list Data blocks
    • The Ext family FS
    • FS structure in Unix
    • The Ext family FS
      • Buffer cache
      • Syncer
      • 13 entries per inode
        • The first 10 direct
        • 11º indirect simple
        • 12º indirect double
        • 13º indirect triple
      • If the block size is 1KB
        • Files of 16TB
  • Other FS
    • Special FS
      • Swap
      • ProcFS / SysFS
      • DevFS
      • TmpFS
      • UnionFS
    • In Unix everything is a file
  • Journalling
    • Avoid corruption
    • Write log before commit
    • Before journalling
      • Guessing work with “fsck”
    • For ext3, two ways of mounting the partition
      • Async: uses journalling and it's faster
      • Sync: old system without journalling, makes changes straight to the disk
  • Journalling
    • Ordered (default)
      • Only log of Metadata
      • Data written to the disc before writing the log
    • Writeback
      • Only log of Metadata
      • Data written to the disc after or before writing the log
    • Journal
      • Log of Metadata and Data
      • First write the log then the disc
      • Slower but the most secure
  • Resources
    • http://en.wikipedia.org
    • http://users.iafrica.com/c/cq/cquirke/fat.htm
    • http://hebb.cis.uoguelph.ca/~dave/CIS275/Lectures/file7.html
    • Old notes