[etbe]

In addition to cables and backplanes that have been mentioned, the entire path from RAM to PCIe to disk controller has non zero risks of errors. That said I'm pretty sure that the BTRFS errors I've seen from SSDs have all been the fault of the SSDs in question.

Also note that hard drives have had internal error detection and correction codes for decades, so SSDs doesn't change things much. Probably most checksum errors are misplaced writes and missing writes.