Yeah, never hardware raid. It’s a disaster waiting to happen, even with expensive dedicated cards.
Easiest is with btrfs raid1, the drives don’t even have to be the same size like in other raid systems. For example you can combine two 2TB drives with a single 4TB drive into one 4TB Raid1 and also remove and change things as you want. ZFS has a few more features but is much more rigid and likely to break on Linux kernel updates as it isn’t part of the kernel like btrfs.