A tale of failures. I wanted to copy a PS4 game I have off the internal hard drive onto a USB drive, so I could copy it onto a second console instead of redownloading 60GB+ worth of stuff. This turns out to be impossible.
Since version 5.50 the PS4 has gotten a lot friendlier about supporting USB drives. Among other things you can relatively easily plug in a USB drive and copy user data (like game saves) to and from it. The PS4 will do this with any exFAT or FAT32 disc, like your garden variety flash drive.
You can also move a game from the internal hard drive to a USB. Key point there: move, not copy. Copy is explicitly not allowed. You can only move a game to disc if the disc is formatted as “extended storage” for the PS4. I thought I’d be clever and move the game to an external drive, make a clone, then move it back. But you can’t do that easily. The extended storage volume doesn’t even have a meaningful partition table, no filesystem I can mount. I suppose I could make a block level clone of the disk but that’s too much trouble. (It’s probably just some slightly bent version of a standard FreeBSD or Windows filesystem, but I’m not going to waste time researching that.)
One last option PS4 supports is to back up your whole console to an external disc, then restore it to a different console. You can also clone one PS4 to another directly over a LAN. However in both cases the destination PS4 gets entirely wiped and reconfigured, it’s not suitable for making a copy of a game.
The stupid thing about all this is Sony probably still thinks it’s doing some useful copy protection. It’s not, the copy protection is entirely keyed now to your online account. They’re just making it awkward for power users to do reasonable things.