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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