Power Redundancy

I've been thankful to be in locations that really haven't had power issues, but despite being in locations that don't have power issues, the power still goes out occasionally. So we definitely want some sort of power redundancy.

Redundancy through the whole path

I want to illustrate this point with a setup that I did a long time ago. These right here are storage area networks, or SANs. Essentially what they are is just a place where you can store things, and we had virtual machines on here. Already you can see that there's one, two, three of them right here, so we already have some redundancy amongst this equipment. But the focus of this is power, so I wanted to show you the redundancy in the power here.

First of all, we have a power supply for this middle one right here. We can see this power supply, so that's one of the power supplies. And then on the other side, which you can't really see as well, it's sitting right here — that's the second power supply. So we have redundancy with the power, by the power supply, on this piece of equipment.

The other thing is, if you follow this power cable that comes from there, if you were to follow it, it comes and plugs into this side of the rack, which is what's called a power distribution unit. And then if you follow the other side, it goes to this side of the rack. You can see this a little bit better — you can see all the plugs into here. So this is a different power distribution unit. Each of these power supplies goes into a different power distribution unit. So we could lose a whole unit here and we'd still be up and running. We could lose a whole power supply and we'd still be up and running.

Now, these go back to a UPS, and we'll talk more about a UPS in a second, but essentially it goes to different UPSs. Those different UPSs are then plugged into different what we call circuits. I don't want to get into a bunch of electrical work and what those are, but essentially they're two different circuits. So we could have a circuit go down, we could have a UPS go down, we could have a power distribution unit go down, or an actual power supply go down, and we'd still be up and running. So all along the whole path, we have redundancy with it.

Power sources and backup generators

Let's talk about power sources. We have backup generators. There is utility power coming into these buildings, supplying us with power from the power company, and so that's supplying us, in this area, with fairly cheap power. We are running off of that power, but it's not perfect and it can go down. As a result, we also have this backup generator. Once the power goes out, this backup generator comes online and starts powering it.

The problem is that there's kind of a lapse between these two. It takes about five seconds for this generator to turn on and spin up — and probably a little bit longer than that by the time it actually switches over to this generator right here. So there's a time involved with that, and that would be an outage. The power company drops off, the generator kicks in, and now we've got this gap of time.

The UPS

So what do we do in the meantime? We've got this uninterruptible power supply, or UPS. I have a rack right here, and you can see there are two units sitting here on the bottom. Those are UPSs right there, and they're supplying power to these different devices on here.

These UPSs are a battery backup, so what happens is that there is no downtime. The power kicks off, these UPSs are instantly turned on, and they're providing power to the equipment, so there is no downtime. Then the generator kicks on and takes over, and those UPSs are no longer needed. So it's kind of this stopgap in between. Now we have redundancy within all of this power.