is there a way to tell that you have ext4 filesystem vs ext3

[Eric Sandeen]

John5342 wrote:
>>In that case is there a way to convert the ext3 to ext4 whilst retaining
>>all the pre-existing files?  If not then would the system be happy having
>>ext4 / partition as well as co-existing ext3 /opt and /home partitions on
>>a single system?
> To the best of my knowledge ext3 can be converted to ext4 simply by
> mounting ext3 as ext4 with only minor limitations (same can be done from
> ext2 to ext3. Therefore formatting ext3 partitions to take advantage of
> ext4 should not be necessary.

That's largely correct.

You can mount any ext3 partition as ext4, but you'll get varying degrees
of ext4 advantages that way.

ext2->ext3 was actually a bit simpler, as ext3 when it was first
introduced really was pretty much just ext2+journal.  There are many
more changes in ext4, many of which have different disk format implications.

ext3 filesystems created in F9 or later will have larger inodes, which
leaves room for some of the new features in ext4.  Simply mounting ext3
as ext4 leaves existing files in the old format... there are conversion
tools for both of these things, but they have not had a huge amount of
testing yet.  There are also mkfs-time geometry changes (flex_bg for
one) which you don't get if you migrate a filesystem.

-Eric