That's why I suggested to try that first using umount/mount to see whether the enry in fstab is correct. You can also change the entry to look like this:
Code:
/dev/sdb1 /mnt/sdb ext4 defaults 0 0
But you should in any case test that before rebooting…
adjust /etc/fstab
umount /mnt/sdb
check that the volume has been unmounted
mount /mnt/sdb
again check that the volume has mounted successfully