I have a UEFI laptop with two disks, /dev/sda and /dev/sdb.
Ubuntu 16.04 is installed on /dev/sdb. There is already an ext4 partition of /dev/sda, but I want anything there to be overwritten.
I wish to install Ubuntu 20.04 on /dev/sda, such that:
1) During a transition period, I can boot from either Ubuntu 16.04 or Ubuntu 20.04
2) After a transition period, I will delete Ubuntu 16.04 from /dev/sdb
3) I don't have to physically disconnect /dev/sdb before doing the installation
I boot the computer from a USB with the Ubuntu 20.04 image on it. When I get to the screen asking for the installation type:
Q1) I presume I should choose "Something else", because installing Ubuntu 20.04 alongside 16.04 will install it on /dev/sdb, which I do not want. Is this correct?
Q2) After selecting "Something else", do I choose /dev/sda or do I choose /dev/sda1 (which already has the ext4 filesystem on it)?
Q3) On the same screen, where I am asked for the device for the boot loader installation, the options are:
/dev/sdb2 Ubuntu 16.04 LTS
Given my goals as described above, which option should I choose?