Depending on your comfort level and setup, you could use LVM. Then the differently sized hard drives wouldn’t be such a problem.
Or if you want a much more complex situation, you could set up Ceph. It will also give you redundancy, but it’s a really steep learning curve.
Or mergerfs if you are not too concerned with performance
Btrfs also allows for mixed size drive. It's the reason why I use it
Edit: autocorrect
I'm on btrfs. I have a 14 TB, a 16TB, and two 7TB drives in RAID1. I'm running out of space for all my linux ISOs and I'd really like to transition to some sort of 3 or 4:1 parity raid, but you're not supposed to use that and I don't see a clear path to a ZFS pool or something
Depending on your comfort level and setup, you could use LVM. Then the differently sized hard drives wouldn’t be such a problem.
Or if you want a much more complex situation, you could set up Ceph. It will also give you redundancy, but it’s a really steep learning curve.
Or mergerfs if you are not too concerned with performance
Btrfs also allows for mixed size drive. It's the reason why I use it
Edit: autocorrect
I'm on btrfs. I have a 14 TB, a 16TB, and two 7TB drives in RAID1. I'm running out of space for all my linux ISOs and I'd really like to transition to some sort of 3 or 4:1 parity raid, but you're not supposed to use that and I don't see a clear path to a ZFS pool or something