Developers deserve to be paid for their time though...
Sure for many it's nothing but a hobby and they're happy to create something for free. But that doesn't mean every developer needs to do the same.
And yes ads are a privacy nightmare and putting them into your app is bad. So either you only use apps from hobbyists or you pay for access (whether that be a set price for a finished product or a subscription for a service).
Btrfs works with different hard drive sizes, with 1 disk failure with no data loss.