but I want the software installed via software Center to be installed in the HDD.
Why? if you think 40Gb is not much: Ubuntu hardly comes above 15, 20GB. But then you should re-evaluate that method and remove software you don't use.
I have a mysql database and apache webserver running on a root with 15Gb. Never have issues with it.
40 Gb is already overkill for the root partition.
To my knowledge, it would be just a matter of creating appropriately sized
/home partitions in the HDD and use the SSD for / and swap, right?
Mind that /var/ is used by some software to store data. MySQL for instance.
But the usage of partitions more than /, /home and a personal data partition is old and no longer optimal.
A / of 15Gb is enough to keep Ubuntu up and running up to the next release.
I would suggest though to keep everything on the ssd except for your personal data and there is a configuration for that (see
~./config/users-dirs.dirs). Keep your system and private separate and it will be ...
- easier to make backups.
- easier to replace the ssd.
- easier to put your personal data disk into another system.
- easier to re-install to a new version (you just add the disk with personal data during installation). Both / and /home will be empty of personal data (I don't even bother upgrading; a reinstall takes me 15 minutes).
- the best way to get the most out of the speed of the ssd.
In my opinion this would suffice:
- ssd: /home of 10Gb; after install remove the normal directories in /home/$USER/ and edit
~./config/users-dirs.dirs to point them to the hdd.
- ssd: / with the remainder of the ssd (ie. 40-10=30).
- hdd: /personal; the complete partition of the hdd you want to use.