I don't think you can easily extend a partition to another physical drive, although I may be mistaken. Anyway, a more straightforward thing to do in this case is to constantly mount a partition from your other drive (say /dev/sdb1) into your filesyste
So to expand root partition I must delete swap device to be able to to use unallocated space and extend non lvm root partition. After deleting swap, root partition will become the last partition on /dev/sda after which we can resize primary partition. Cur