Red Hat ENTERPRISE LINUX 3 - INTRODUCTION TO SYSTEM ADMINISTRATION Administration Manual page 169

Chapter 8. Planning for Disaster
Note
Strictly speaking, this approach to calculating VA is not entirely correct; however, to get the true VA
you would need to know the power factor for each unit, and this information is rarely, if ever, provided.
In any case, the VA numbers obtained from this approach reflects worst-case values, leaving a large
margin of error for safety.
Determining runtime is more of a business question than a technical question — what sorts of outages
are you willing to protect against, and how much money are you prepared to spend to do so? Most
sites select runtimes that are less than an hour or two at most, as battery-backed power becomes very
expensive beyond this point.
8.1.3.2.3.3. Providing Power For the Next Few Hours (and Beyond)
Once we get into power outages that are measured in days, the choices get even more expensive. The
technologies capable of handling long-term power outages are limited to generators powered by some
type of engine — diesel and gas turbine, primarily.
Note
Keep in mind that engine-powered generators require regular refueling while they are running. You
should know your generator's fuel "burn" rate at maximum load and arrange fuel deliveries accord-
ingly.
At this point, your options are wide open, assuming your organization has sufficient funds. This is also
an area where experts should help you determine the best solution for your organization. Very few sys-
tem administrators have the specialized knowledge necessary to plan the acquisition and deployment
of these kinds of power generation systems.
Tip
Portable generators of all sizes can be rented, making it possible to have the benefits of generator
power without the initial outlay of money necessary to purchase one. However, keep in mind that
in disasters affecting your general vicinity, rented generators will be in very short supply and very
expensive.
8.1.3.2.4. Planning for Extended Outages
While a black out of five minutes is little more than an inconvenience to the personnel in a darkened
office, what about an outage that lasts an hour? Five hours? A day? A week?
The fact is, even if the data center is operating normally, an extended outage will eventually affect
your organization at some point. Consider the following points:
What if there is no power to maintain environmental control in the data center?
•
What if there is no power to maintain environmental control in the entire building?
•
What if there is no power to operate personal workstations, the telephone system, the lights?
•
157