Design resilience involving availability classes is our next focus. From ISO
22237 documentation, we have what are called availability classes, and they
number four. They are connected to power distribution and have the ability to
maintain resilience during disruption.
Class 1 signifies a single path that has no resilience or
no redundancy, so when planned maintenance or unplanned
outages cause service outage, it's dependent on that single system.
In a Class 2 single‑path resilience,
you have components within devices that are resilient.
We'll see that in just a moment illustrated by means of a switch.
In Class 3, you have multipath resilience, and this is provided by redundant
systems, so then you have concurrent capability to repair,
operate, and to solution based off of separate controls and separate
paths. In a Class 4, Now you have a multipath fault tolerant, where
your redundant systems are actually active in the processing. So Class
3 could be viewed as active/passive, whereas Class 4 would be
active/active. If you were to look at Uptime Institute's view of what
the data center looks like, the data center site infrastructure
standards are in tiers.
They have an unbiased international advisory organization that provides
the baseline that many enterprises use to rate their data centers. In a
Tier I classification, you have no redundancy,
but there is a requirement for dedicated uninterruptible power supplies and 12
hours of on‑site fuel storage. In a Tier II environment,
you have the capacity components that are redundant within a
system, but you don't have redundant systems. In a Tier III,
you have redundant systems,
one of which is active and the other one is passive. And in Tier IV,
you have an active/active environment for systems. These make a
direct parallel to what was described in the Class systems of ISO
22237, but let's see what does this look like if we were to actually
visualize a system.
So, in this example, we have a data switch. In a Tier I
environment, you have no redundancy.
So let's say that this switch then had a management interface labeled
Interface 1 and a power supply labeled Power Supply 1.
If there were failures in the interface or failures with the power supply,
that's it, there's nothing left. In a Tier II environment, now it's still a
single switch, but you have redundant capacity components.
See the picture? Tier III, now we duplicate the redundant switch and we
actually make it so that one switch is processing actively and the other
switch is not processing actively. In a Tier IV environment, we move from
active/passive to an active/active environment, where we're actually
processing with both of them.
Now, while you may get performance gain, that is not the purpose.
Remember, our focus is on availability classes.