Linux HowTo: File system Organization on Disk

Today, discussing some File system related concepts - inodes, Device Files, Superblock, Journaling etc.
Lets get started..
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What is an inode?
-inode = stores info about a file location on disk and its attributes.
-an inode points to either:
    -another inode    or
    -a data block
-inode contains:
    -file owner
    -permission
    -size of file
    -creation time
    -last access time
    -group id
-Note:    inode does not have file name    -    this is so as to permit an inode to point to multiple inodes.

-hardlink    -    two files with same inode; their names may be different but they point to same disk location. cant span fs (as different fs have separate inodes)
-softlink    -    two files that refer by name instead of inode. ie their inode values are different. they can span fs.
    [ To remember, hard same inode = hsi ]

What are Device Files?
-Device files are special files for organizing data in Linux (and Unix) OS.
-block device files:
-device driver files to interface with devices in blocks of data.          Their first char is 'b' in ls -l      (eg ls -l /dev/sda1)
-block device files have two numbers - major and minor.
    -major block device file number    -    points to the driver
    -minor block device file number    -    points to the interface.
-eg:    if /dev/sda1 and /dev/sda2 have different interface ports but share the same driver, then they will have same major number but diff minor number.
-character device files:
    - device driver files to interface with devices as one char of data at a time. Their first char is 'c' in ls -l    (eg ls -l /dev/tty1)   
    - they too have a major and minor number like block files.
Note:    from man pages, mknod cmd is used to create block or char device driver files.
Note:    from experiment, mv preserves inode number, cp creates new inode.

-sync    = writes disk cache to be written to disk;

What is a Superblock?
-superblock   
    -the first piece of info read from disk.
    -it hold info about:
    -location of first inode
    -amount of space
    -disk attributes
-without a superblock, data on disk is useless. that is why multiple copies of superblock are maintained.

Why is Journaling of FS important?
-ext3 is enhanced ext2 with journaling.
-journaling helps keep track of bad blocks. so fsck does not have to be run after every crash.
-the journal keeps track of changes like a redo log. it writes only when commit happens.
-so data is cleanly written or not written at all--thus avoiding corruptions during crash--this increases integrity and avoids fsck to be run. this saves time.