Migrating to EXT4

Ext4, the successor to ext3 which was formerly known as ext4dev, is marked stable in Linux kernel 2.6.28, meaning the Linux kernel team now recommends using ext4 in production.

To convert a file system from ext3 to ext4, use

tune2fs -O extents /dev/DEV

and remount the file system as ext4. (Two e2fsck runs are recommended before and after tune2fs.) Some documentations also include the -E test_fs option. This is not necessary now since ext4 is no longer experimental.

Finally do not forget to modify /etc/fstab.

An ext4 file system created this way is not a “true” ext4 - the extents feature, the main advantage of ext4 comapred to ext3, is not automatically applied to old files. New files created afterwards are in the extents format.

Unlike the 100% backward compatibility of ext3 with ext2, an ext4 file system can no longer be mounted as if it were an ext3, unless the extents feature is disabled. (If you want to disable extents, why not simply use ext3?)