HDDs also use ECC hence why read errors occur on failing drives instead of just silently returning corrupt data. That's not an ironclad guarantee and plenty of

HDDs also use ECC hence why read errors occur on failing drives instead of just silently returning corrupt data. That's not an ironclad guarantee and plenty of places in the data path can let an errant cosmic ray flip bits. BTRFS doesn't even eliminate this, it just reduces the surface area and most importantly gives you a way to durably detect or correct this from when the checksum is generated in the kernel onwards.