If you haven't looked into it, and if you already have the disks of varying capacity, check out JBOD. You will have to configure a system for backups however as you wont have parity like raid1
I'm aware, but raid 1 is mirroring which is redundancy, a jbod offers no redundancy so a backup would be even more crucial to protecting from data loss. Also i never said raid is a backup.
Don't know myself as I have no use case for that setup, but it is a well known setup since several years. If teh performance was bad it wouldn't be recommended as an alternative as often.