# Redundancy = N + WHAT?!?

1N, 2N, N+1, 2N plus one, N plus 1 + S, N plus… what the heck are you talking about?!?

You’ve probably heard a term thrown around once or twice called “N. ”

So N+1, 2N, 2N +1, my personal favorite N+1+S… What the heck is N? And how does it apply to you?

So N is the number of critical devices that you need in order to run your infrastructure, so it usually refers to power infrastructure and UPS modules, but you can apply this to basically anywhere in your infrastructure stack: so routers, firewalls, switches, servers, etc.

N connotes the number of devices that you need in order to run. So you need one server, that’s a single N.

So now we get into N + 1, so N + 1 is the number needed to run plus one spare. 2N is twice the number that you need to run, and 2N + 1 is twice the number that you need to run plus a spare.

Now let’s make an example here:

I have two toddlers, so in my world if you need a digger toy, so in my case single N is 2 digger toys. Well, now you want to have redundancy because what happens if you lose a digger toy? Well now you need 3 digger toys: that’s N+1. 2N my world would be four digger toys, and then 2N+2 would be 5 digger toys.

Or you think lovey blankets: now if I had three children, 3N would be 3, 2N would be 6, 2N +1 would be 7 of these digger toys or seven lovies.

So depending on the actual requirement that you have for redundancy, looking at whether you need to be N+1, or 2N or 2N+1, that has direct impact on your cost as well as your availability. Now my personal favorite and all this is N + S or N + 1 + S and so + S is a cold spare. So I just call it a cold spare.

So we do a lot of assemblies, where we’ll do -instead of high availability where we’ll have two devices online at the same time- we will have a cold spare.

We will have a box, unplugged, sitting in inventory that’s ready to go and ready to configure, so N+1+S, so a redundant unit with high availability plus a spare or just N + S in a lot of cases is really good for people.

**Why would he do it this way?**

Redundancy introduces complexity, so as you add more and more and more devices to your environment that have to fail over and have high availability and have to dynamically reconfigure themselves or whatever else needs to happen for this redundancy, it adds a lot of complexity to your environment. And you’ve probably seen these topology maps where there’s boxes all over the map and all of a sudden you start drawing these lines through them in order to connect all of them, and that’s what’s necessary for redundancy.

So if you get rid of all those things, you say, “We have one box and then we have one spare box,” your environment’s really simple.

So moral of the story: if you are trying to figure out how much redundancy you need and what actually makes sense for your operations, do you need just N? N+S? N+1? N+1+S? 2N+1? whatever the actual things are, give us a call at ITBroker.com we’ll talk to you about your business, we’ll understand what makes your business unique and your operations unique, and we will match the appropriate level of redundancy for your infrastructure to your actual needs.