[ Thanks to Mike
Weber for this link. ]
“What is ext4?
The ext4 file system is a journaling file system which is a branch
of ext3. Ext3 has been so valuable in terms of stability and
usability to Linux that the developers decided to fork ext3 to ext4
instead of incorporating the features of ext into ext3. Those
features include 64-bit storage limits and performance boosts. The
2.6.28 Kernel included ext4 as stable code.Advantages of ext4.
The advantages of ext4 are two. Ext4 has increased filesystem
support for volumes up to 1 exabyte, with files up to 16 terabytes.
In addition, ext4 has increased performance. Currently, ext
supports 16 terabyte filesystem and 2 terabyte file size.“Ext4 uses extents, which are a contiguous range of physical
blocks on the hard drive. The key word here is contiguous, as you
can see in the illustration the blocks are close together. The
advantage is large file size performance and the reduction of
fragmentation because your data is placed in a more centralized
area. A extent can be up to 128MB of contiguous space with 4KB
block size. If you choose to use extents in ext4 you will not be
able to go backwards to ext3 as the extents are not compatible with
ext3.”