Is it important for you to know about your partner's past relationships?

We frequently get into discussions where he voices his discontent with "all the unknown". On the other hand, I am rather uncomfortable knowing so much about his past and am confused as to why he wants to know things like that about mine. I've told him how many people I've been with and that's about it- no need for names (he wouldn't know them anyway) and descriptions as I'd care to not remember them. I choose not to talk about it bc, quite frankly, I don't want to. So, I'm curious to see other people's take on this. How much do you want to know about your partner's past? Would you be upset not knowing much about it? Is it important for you to know?