If I had to do encrypted btrfs RAID from scratch, I would probably:
- Set up LUKS on both discs
- Unlock both
- Create a btrfs partition on one mapper
- Add the other with
btfs device add /path/to/mapper /path/to/btrfs/part
- Balance with
btrfs balance start -mconvert=raid1 -dconvert=raid1 /path/to/btrfs/part
- Add LUKS’ to crypttab, btrfs partition to fstab and rebuild/configure bootloader as necessary
In that scenario, you would probably want to use a keyfile to unlock the other disc without rentering some password.
Now, that’s from the top of my head and seems kinda stupidly complicated to me. iirc btrfs has a stable feature to convert ext4 to btrfs. It shouldn’t matter whatever happens outside, so you could take your chances and just try that on your ext volume
(Edit: But to be absolutely clear: I would perform a backup first :D)
It depends on the brand I guess. Some Canon Pixma did immediately worked with my distro, like literally zero setup required. However, it refuses duplexing. It just won’t do it. Not driverless and not with gutenprint, although it lists the specific model, not when setting it as the default, not when setting it per job.
Yet it works on Android no problem.