You may need to force mount. And it is ext4, not ext2, I think.
mount /dev/sdb4 /media/external -o force
If that does not work, you may need to start RAID on your system and add the drive to RAID using mdadm
You may need to force mount. And it is ext4, not ext2, I think.
mount /dev/sdb4 /media/external -o force
If that does not work, you may need to start RAID on your system and add the drive to RAID using mdadm