- [Instructor] In this video,
we want to consider fabric capacity planning.
And when we talk about fabric,
we're normally talking about,
the network interconnections inside of a data center.
Earlier, we considered a spine leaf design
that we might have in a data center,
where we have our servers connected to leaf switches
and the different leaf switches,
they're pushing data through spine switches.
And let's say that we're trying to select
an appropriate spine switch to handle the capacity
of a certain number of leaf switches
and a certain number of servers,
well we've got some questions to ask.
The first question might be,
how much data do we need
to push through a data center switch?
If we're talking about a spine switch,
we need to consider
how many leaf switches we're connecting to,
and how much data is going to be flowing in that maximum
from all of these leaf switches.
We have to get this number if we already have a data center
in place and we've got a baseline for that data.
Hopefully we've got some historical data as well,
we can look at trends over time to forecast
what future bandwidth demands might be.
But if we don't have the luxury of all that historical data,
we could at least in an existing design,
look at some interface counters over time,
maybe a few days.
And we could come up with a pretty good guess as to
what the maximum amount of bandwidth is,
that's going to be passing through one
of these spines switches.
And when we're selecting a spine switch,
we want to ask how much data can we push through
that hardware platform?
That's a big part of fabric capacity planning,
we want to see what is the capacity of this spine switch,
which is really going to be at the center of our fabric.
And we want to think about not just what meets today's needs,
what about the future?
How long are we going to keep this spine switch?
Three years, four years.
Over that time, do we anticipate the bandwidth demand
to grow and if so by how much,
and using whatever data we have available
or whatever data is forecasted for the future,
once we have our best guess as
to how much bandwidth
is going to be pushed through a spine switch.
Let's take a look at how we might see
if a spine switches up to the task.
And just as an example,
I'm going to be using an 18 slot Nexus 7000 series switch.
And in this 18 slot switch,
we're going to have a couple of supervisor engines
and the rest of the slots are going to be input output
or IO slots.
And here's the formula for how we calculate
that switch's bandwidth capacity.
We're going to see what the inter-slot switching capacity is.
And we'll need to turn
to the hardware documentation for that number.
And we'll take a look at that in just a moment.
And then we multiply that by the number of IO slots,
which is going to be 16 in the switch that we're using.
And we're going to add to that, the throughput
that we can get through the supervisor engines.
But notice the formula I have here,
I'm saying what is the number of supervisor engine modules
and we're multiplying
that by the inter-slot switching capacity,
but then I'm dividing by two.
Why are we dividing by two?
Well, I'm dividing by two because,
a supervisor engine is going to have half the capacity
of a regular IO module.
That's the reason we're dividing by two.
Now again, this is going to vary widely depending
on your particular switch model.
So be sure and check your switch's documentation.
But for this 18 slot Nexus 7000 series switch,
here's a documentation page showing that,
the maximum inter-slot switching capacity
is a 550 gigabits per second.
And we've got 16 IO slots and two supervisor engine slots.
So let's take those numbers
and do some insertion into our formula.
We know that the inter-slot switching capacity
is 550 gigabits per second,
we know that we've got 16 IO slots,
we know that we've got two supervisor engine modules,
and we're going to take the inter-slot switching capacity
of 550 and multiply by two,
but then we're dividing by two because,
those supervisor engines they have half the throughput
of an IO slot.
And if we do that math,
we come up with 8800 gigabits per second,
plus 550 gigabits per second
for our two supervisory engines.
And if we add those up,
we get 9350 gigabits per second.
Just over 9.3 terabits per second.
But this calculation doesn't consider
that we're going to be running in full duplex,
which almost definitely we are.
So to get the full switch bandwidth capacity,
if we're running full duplex where we're transmitting
and receiving simultaneously,
we need to take this number and multiply by two,
that means our full duplex switching bandwidth capacity
is a whopping 18.7 terabits per second
for this particular model of spine switch,
and we need to take that number and see
if that will accommodate our projected future growth
of our bandwidth needs going between our leaf switches
that will be flowing through this spine switch.
But maybe this is way too much.
We don't want to spend a lot of money
on bandwidth capacity that will never use.
So we can try a different model of Nexus 7000 series switch
as an example.
And we can look at the documentation
and go through the same calculation
and try to come up with a switch model
that will meet our current and future needs,
while not costing us more money for bandwidth
that we'll never use.
And that's an overview
of how we can do fabric capacity planning.