>> Let's switch gears a little
bit and start talking about what
happens when things go bad for good network admins.
Regardless of what incidents happen on the network,
all management and fault tolerance
is always going to be essential.
When we talk about fault management,
we are really talking about
being able to withstand failures
of one or multiple devices and
>> continue to move forward.
>> Do we have the redundancy in place?
Do we have the capabilities to keep
moving forward as an organization?
At first, when we're planning for redundancy,
we have to have some idea
>> of how much redundancy we need.
>> How much is enough?
There are a couple of terms,
a couple of metrics that may be helpful.
The first is a key performance indicator, KPI.
The key performance indicator will give
us an idea of whether or not a device is
performing to its expectations
because rarely does a device just stop working.
Often, the service starts to
degrade and we start to see some issues come up.
If a specific device isn't
meeting its standard performance,
that might be an indicator that we're looking
at a device that's getting ready to fail.
There are also metrics that the vendors give to us.
One is mean time to fail and
>> mean time between failures.
>> These are pretty comparable,
but the idea is mean time to fail
indicates this is a device that we don't repair.
This is the lifespan of the device.
We're going to buy it,
three years later it's going to fail.
Mean time between failures gives
the indication that the device can be repaired.
We buy the device,
it goes three years, it fails,
we repair it, three years later,
it fails, we repair it, and so on.
Then we've also got to consider how
long it takes us to repair the device,
which is mean time to repair.
If it's going to take us a long time
to repair the device,
is it possible that we can just replace it?
A lot of these, we don't really repair
a whole lot of devices today because
most of them can be replaced much cheaper
than the time and effort it would take to repair them.
The last are service level agreements.
Vendors are going to provide us with
commitments as to performance and availability.
A lot of times that revolves around up-time.
For instance, if I'm storing
my data with the Cloud service provider,
the redundancy is up to them
so that way they can meet their metrics.
With redundancy, we want
a redundancy to be comprehensive
and not just focus on
just redundant data or just redundant drives.
We really want to make sure that all of our areas are
redundant because a chain is
only as strong as its weakest link.
We start off by talking about redundancy in servers.
That's just multiple servers performing the same role.
This is not the same as a cluster
because with redundant servers,
each server is its own unique device.
I have domain controller A,
and domain controller B,
or DNS 1, DNS 2.
If one fails, the second is
up and running and is available.
A cluster. I have
multiple physical nodes acting
as a single logical entity.
They are very tightly coupled.
For instance, if I have a cluster or a server farm,
as you sometimes hear them,
you're not going to be able to differentiate
between the servers.
When I go to amazon.com,
there are many hundreds of
machines responding to web queries.
I don't know which one is which because they are
functioning as part of the same cluster.
Clusters also usually do provide load balancing,
but you can also have clusters that don't load balance.
They're just simply working for fault tolerance.
In a smaller environment,
I might have multiple servers.
They can either both be responding
to requests or one could be
passive while the other is
>> the primary responding server.
>> There are all sorts of configurations,
but the real purpose and the
>> real important piece is that
>> we need our fault tolerance for those servers.
That's where your services run.
That's where our resources are.
Many times we use spare equipment.
I have a Switch in the closet.
When we talk about cold spares, that's exactly it.
I've got a device somewhere in the closet.
>> I can find it.
>> I can install it.
>> We often have warm spares, which
>> you're ready to go very quickly.
>> Hot-swap or hot spares are
already installed and it's just a matter
of switching over to them.
Depending on the value of what's being protected,
how much downtime we can tolerate is going
to determine what types of spares we have.