May be I was unclear. If we introduce record abstraction for file ops then OS low-level implementation have to decide which way to store structured data. meta + payload or meta separated from payload. In latter case there is no way to provide fast record streams. Former case does not allow fast byte streams. Client decision to receive bytes or records doesn't magically zero copy reorder stored data.

Why would the later cause record streams to be slow? Snapshots in COW FS' aren't that terribly slow either, even if there is quite a few of them, which basically boils down to the same structure, really.