Just keep using the disk icon.
Just because the original reference is outdated doesn't mean it's useless; the symbolism carries over. Changing it to the sake of future-proofing makes no sense because everybody already understands it now, and that knowledge will carry forward into the future. It has become the standard, even if it makes no sense, it even if it never made sense.
Horsepower is still used to refer to engine strength, even though nobody uses horses. Qwerty is still the keyboard default even though it's not optional, because typewriters had settled on that standard ages ago. The human skull symbol is commonly used as a shorthand to indicate a substance is poisonous, because it has been for a long time. Even the term "dial" when referring to phone calls is still commonly used, even though nobody but your great-grandmother still even owns a rotary phone.
Tldr; If it ain't broke, don't fix it.