Media for 3D optical data storage have been suggested in several form factors: disk, card and crystal.
A disc media offers a progression from CD/DVD, and allows reading and writing to be carried out by the familiar spinning disc method.
A credit card form factor media is attractive from the point of view of portability and convenience, but would be of a lower capacity than a disc.
Several science fiction writers have suggested small solids that store massive amounts of information, and at least in principle this could be achieved with 5D optical data storage.