Some RAW formats are pre-compressed, usually with very simple (hence fast) algorithms, and some aren't even lossless (Sony ARW). It's often possible to further

Some RAW formats are pre-compressed, usually with very simple (hence fast) algorithms, and some aren't even lossless (Sony ARW). It's often possible to further compress them with specialized tools. Disclosure: I'm the author of PackRAW, a tool that does exactly that (https://encode.su/threads/2762-PackRAW https://encode.su/threads/2762-PackRAW)