There are many different types of RNA with different purposes. They all act in concert to produce proteins. mRNA encodes proteins, tRNA brings the proteins into transcription, rRNA actually acts as a protein itself to help drive this machine.
DNA is environmentally sensitive and it can be altered. Your entire genome is not being produced all the time. Different proteins are copied based upon the conformal structure of DNA which changes based upon the cellular environment. The entire structure is copied often and no one particular set of DNA in your body is "the original."
It has aspects of long term storage but then it's utilized in a way that long term storage almost never is. And all cells get their own copy which may be unique in several ways. So RAM seems like a better metaphor to me.