How to mount an internal HDD on start-up?

Solution 1:

You can add an entry in fstab to auto mount your partitions at Ubuntu startup. you can read more about fstab at Ubuntu Wiki

Solution 2:

I'd suggest using PySDM if you aren't looking to manually edit configuration files.

PySDM is a Storage Device Manager that allows full customization of hard disk mountpoints without manually access to fstab. It also allows the creation of udev rules for dynamic configuration of storage devices.

In Ubuntu, it can be installed by searching the Ubuntu Software Center for "pysdm". Once installed, it is available under the System --> Administration --> Storage Device Manager.