Yes, you are right, they use raw lz4 and don't do checksumming there. And I can only find checksumming in superblock code and volume geometry code in vdo reposi

Yes, you are right, they use raw lz4 and don't do checksumming there. And I can only find checksumming in superblock code and volume geometry code in vdo repository. So it doesn't look like they do it on regular data blocks at all, probably just assume you have a properly working FTL. (by the way, sha256 is a slow cryptographic hash, not a checksumming one, like crc32)