I am running Ubuntu's latest LTS. In /dev/sda I have sda1 and sda2, both are using a couple hundreds of MiB with a couple of GiB allocated. So far so good.
In /dev/sdb I have just one partition, sdb1 - using over 300 GiB, about 98% of the available space.
I have about 350 GiB of unallocated space in /dev/sda - what is the easiest way to both move it from sda to sdb and allocate it?