I’m currently using a 2TB drive with btrfs where I’m running out of space.
I have a different 1TB drive that I’m currently not using.
I see two options:
Format the 1TB drive and mount it somewhere so that I can store things on it. It’s probably the easiest solution, but I don’t like it because I wouldn’t use the available space to it’s full potential.
Add the 1TB drive to a btrfs pool and have a combined 3TB drive. I like this option, but I’m not sure if this is actually a good idea. I’ve read things about issues with some forms of configuration, and I’m not entirely sure if they apply to what I want to do.
I would not do that. Putting two devices in one RAID0 actually doubles the failure probability. If either drive A or B fails, the whole pool is gone.
I would rather leave them as separate drives and do a “manual load balancing” by moving folders / subvolumes / mountpoints from one drive to the other. With such a setup both drives are independent from each other and if drive A fails you still have drive B.