Hello newbie here,
In my fedora desktop i have 5 storage devices:
500gb ssd with windows kvm
500gb ssd with boot efi and root partitions
1tb ssd with /home partition
1tb ssd with flatpak_apps partitions (i mounted this in /home/nico/.var)
2tb hdd empty (no partition or anything)
All the drives use btrfs and are encrypted with luks2.
My question is: How can i use my 2tb hdd to add redundancy to the data in the /home partition and root partition?
I haven’t done it, but I expect that you would need to create partitions on the new drive that are equal in size to the partitions that you want to mirror, then use btrfs device add ... to add the new partitions to your existing Btrfs volumes, then (apparently) there is a command to tell Btrfs that you want the data mirrored across the backing devices/partitions: btrfs balance start -dconvert=raid1 -mconvert=raid1 /path/to/mountpoint.
I would suggest experimenting in a throw-away test environment before trying anything like that on your real PC.