bcachefs supports both metadata and data checksumming - crc32c by default, but stronger checksums are available as well. Enabling data checksumming incurs some performance overhead - besides the checksum calculation, writes have to be bounced for checksum stability (Linux generally cannot guarantee that the buffer being written is not modified in flight), but reads generally do not have to be bounced.

Checksum granularity in bcachefs is at the level of individual extents, which results in smaller metadata but means we have to read entire extents in order to verify the checksum. By default, checksummed and compressed extents are capped at 64k. For most applications and usage scenarios this is an ideal trade off, but small random O_DIRECT reads will incur significant overhead. In the future, checksum granularity will be a per-inode option.