It's highly recommended to backup the whole partition, or at least copy the files from the efs directory.
CORRUPTED OR NOT?
You can check if the efs is mounted or completly damaged with this command:
You will see something like this:
Red part means /efs is mounted.
IF YOUR PHONE HAVE CORRECT EFS PARTITION:
1, Root your phone - there are several methods to do this.
2, Install root explorer or Estrongs file explorer and copy /efs dir to your sdcard - this will copy the files.
2, Make a backup from the whole partition -this is better if you flash a phone with wrong ops, the only way to restore using this backup.
dd if=/dev/block/stl4 of=/sdcard/efs.rfs
Add efs.rfs to an unix compatible tar and flash with odin as efs file:
IF YOUR PHONE /EFS IS CORRUPTED:
Flash the included /efs tar with odin:
This will remount your efs partition and (if you have a backup or fixed nv_data.bin) you just need to overwrite files with a file explorer.