It is certainly more overhead when you have to keep a journal for each disk and a checksum for each cluster on each disk instead of one checksum per stripe or e

It is certainly more overhead when you have to keep a journal for each disk and a checksum for each cluster on each disk instead of one checksum per stripe or extent and a per-filesystem journal. In other words zfs and btrfs incur less overhead by having the raid, checksumming and journalling layers talk to each other. Implementing them separately in as in device-mapper comes with inefficiencies.