"If you have spent enough time around Linux it's almost certain
you know about the file systems ext2 and ext3, and have probably
heard of ext4. Get ready to hear some more.
"On October 11, 2008, the "experimental" label for ext4 was
removed. While this doesn't necessarily mean that you should change
all of your file systems over to ext4 immediately, it does mean
that you should consider using ext4 moving forward. With the
"experimental" label gone and openSUSE (among others) considering
it for the default file system in a late-2009 release, it's a good
time to review ext4 so you have a solid working knowledge of what
it is and what features it brings to the table."