Which ext4 features are missing on an upgraded filesystem?

Which ext4 features will be missing on a filesystem upgraded from ext3 to ext4 using the instructions here?

The text explains:

There are additional ext4 features, such as flex_bg and > 16TB filesystem support that can only be enabled at format time via mke2fs.

The "such as" implies there are other features too. Does anyone know of a list?

Solution 1:

extents are one of them too, only new files will be created in extents format. In any case if you can reformat the partition rather than upgrade it, it's better to do so, fragmentation will get back to approximately 0 whatever the amount you have on your ext3 FS now.