I am wondering the same, as I have two 16gb optane drives that im not overly sure on how long they will last, but running them redundantly will be the only use I can think of for them currently, where if one does fail it wont really impact me.
I have run into storage space limitations previously on Proxmox, but I will probably run this pretty standalone as a NAS if possible and use other debices for other services anyway, so 16gb being actually useable seems ideal.