How much information can the brain hold?

I’ve often wondered that. Is there some kind of limit to how much you can remember? I mean, yeah, you forget things but then you can be reminded or promptly go, “Oh, right! I remember when that happened!” But then I think about those rare people who can actually remember every single second of every day of their lives. How have they not gone crazy? How have their brains maintained all that information? Let’s assume you were able to live forever – wouldn’t your brain at some point reach a limit for the amount of things you can recall?

It’s hard to say, I mean it’s not like you can say “It can hold the equivalent to 15 billion GB” or something like that. How can you even quantify “how much you can recall”? Number of cells or neural connections or something like that?