Redundancy vs Resiliency

What’s your biggest concern

about technology?

1That you’re going to

spend a lot of money.

2That it’s going to be

broken more often than it’s working.

So what you’re seeking is a highly available solution.

The problem is, you can’t buy a box

of availability…

You have to build it.

Redundancy

Everyone gets redundancy.

It’s two of something.

ChassisModules

Links

2 Tacos

A backup for the primary if it fails.

Here’s an example.

We have redundant cables connecting the

buildings together.

If one cable fails, we can use the other!

But what happens if a back-hoe takes out the conduit that houses both

cables?

Our redundancy was defeated by a single

event.

This is where Resiliency comes in.

Resiliency builds on top of Redundancy.

Resiliency provides the ability to…Recover, Converge

Self-Heal

So let’s update our example with some resiliency.

Now we can lose a conduit or a cable, and our

redundancy survives.

So what are some additional things we can

do inside the building?

Ensure separate demarcation entry points for power,

telecommunications and data.

1

Create separate cable paths within the building.

2

Keep redundant hardware in separate rooms within

the building.

3

Keeping redundant hardware in separate rooms

is GOOD.

Distributing redundant hardware

across the two buildings is BETTER.

The goal is to ensure that no single event can

defeat our redundancy.

So with redundancy and resiliency, we have a bulletproof physical

design.

Cool… we’re done,right?

Not exactly.

This is a great foundation. But…

We still need to talk about the traffic flowing across the link…

Here, traffic is balanced and performance

is excellent.

But when link A fails, all of it’s traffic goes to link B.

Now we have too much traffic on link B and performance is poor.

By introducing logical resiliency, we could have

avoided this problem.

Quality of Service (QoS) would allow us to permit business critical traffic

ONLY…

These guys don’t count as business critical traffic.

Now, if a circuit fails, we have plenty of bandwidth for our

business applications.

At this point, we have a RESILIENT solution.

All too often, the focus is REDUNDANCY, with RESILIENCY

getting little to no love.

To achieve high availability, the design MUST be resilient.

Resiliency automatically includes redundancy.

And there are many, many

layers to a network.

Design Matters

Redundancy and resiliency are the key to success in

your network design.

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