There should be a Moore law of memory

Is there a Moore law of memory? Because if there isn’t there should be one. It should read like this: every 18 months you can buy twice the memory for the same price. And this Moore law of memory is finally working in my favor. As opposed to Moore law itself which seems to be a wash because whenever you get faster chips you get bigger programs, with storage memory I am now unable to produce content at the speed hard drives are falling in price. All my photography and videos taken throughout my life amount to around 3TB. Now that I take RAW photography and HD videos I consume around 100GB per month of memory. But I saw that now they make 6GB external HD for around $400. I am about to get one of those, I can put everything I ever photographed or filmed and still have enough room for a couple of years. It feels nice to be ahead.

In any case advice on what HD to get is appreciated.

• Memory
• Photography