PS4 Backup file size?

Quick, silly question. If you do a backup of your PS4 using the "Backup and Restore" method, is the file size going to be the same as the used space on the PS4? (500GB used = 500GB file size?)

Or if you have, say, a 2TB drive that's less than half full and you back it up with the backup utility, can it only be restored onto another 2TB drive, even if the used space would fit on a smaller drive?

Thanks!