If I create an ext4 filesystem on top of a zfs ZVOL and add a line to /etc/fstab for it: Then mount /mnt/zvolname will work just peachy. HOWEVER, trying to boot the system results in a hang, because ...

I have an almost full 2Tb removable drive that has recorded TV programmes over many years. The file format for my recorder saves the programmes in the EXT4 format. I have no experience of Linux but ...