There are many ways to partition drives for limited space.
Manual partitioning:
Look in the root partition ( / ) and you will find several directories that can be put on separate partitions for the exact problems you are having (as well as for other reasons).
My new ubuntu install (Bionic) currently uses about 6 GB of space. On my newest laptop, when looking at the output of du I find that /var uses about (at present) 30% of the 6 GB total.
The users home directory tree ( /home ) often uses a considerable amount of space as well. Om my main computer I have 3 TB allocated to /home and am using more than half.
Both /var and /home can be quite volatile in space demands and when the primary installation partition is limited those two can (and probably should) be placed on another partition to distribute space requirements.
In the early days when disk drives were expensive and space was at a premium it was found necessary (for servers) to place /var on its own partition because mail, software cache, files being served, etc would fill up the space and cause a system crash if no space was remaining for the OS partition. Malicious individuals would deliberately shut down ISPs and others if they were not prepared for such an attack.
LVM:
If you are using LVM to manage your disks, changes can be quite painless.
If you are doing it manually some careful planning and partitioning in advance can easily distribute the data to manage disk space as well. Changes without LVM are painful.
Having both drives (or at least the used 30 GB of drive 1 and all of drive 2 ) as part of an LVM will allow seamless usage of the second drive as space demands.
As a side note:
You did not state what you are using the original 70 GB of the ssd for. If I correctly assume that it is a install of another os then it is probably not movable. If it is purely data then it could easily be relocated.
Good luck!
BTW,
Some things are accessed frequently and speed becomes a factor. Others are read by the system once or very infrequently and for those speed is really immaterial.
mount
command, and learn how to edit /etc/fstab. Go ahead and try it and learn. #2 is simpler if you need more space today, or if you are unwilling to learn. Beyond that, it's a matter of preference. – user535733 Feb 04 '19 at 01:17