"Chris Samuel: ext4 is a much bigger change from ext3 than ext3
was in turn from ext2. Ext3 essentially just added journalling to
ext2, whereas ext4 moves to an extent based filesystem with other
features such as delayed allocations (like XFS) to allow the
allocator to be more intelligent about how it lays things out on
disk and much bigger filesystem sizes (though the programs to
create ext4 filesystems can't actually make them for you yet).
Another nice feature is the fact that the journal data is
checksummed so the filesystem can spot any corruption after a
"So the upsides are all the new features, but the downside is
that there is an awful lot of new code here and while it has been
in the kernel for a while marked 'experimental' it's not had the
years of testing and hardening that ext3 has gone through."