I have been trying to do this setup right but it just doesn't work as I would wish to. First thing, I'm legacy, bios and have MBR so number of max partitions is 4. I already have 4 so it displays the 5th one I created for ubuntu as "unusable". So my goal is to take a partition from the second drive (Disc D) and install Ubuntu there. I tried the MBR to GPT conversion, seems like my laptop doesn't support it, which is weird since it's not that old of a laptop (Dell Inspiron 5559) Any help?
sudo parted -l
converting from MBR to gpt normally erases drive. But you can convert in place, but either way you need good backups of data on drive. And good backups whenever making major changes to system. Converting to or from GPT - must have good backups. rodsbooks.com/gdisk/mbr2gpt.html