better suited for the specific requirements of each business case. These
options include:
• Cold restoration, when no alternative failover resources are kept run-
ning. This requires a complete rebuild of the application and data envi-
ronment (preferably via automation). Because no failover resources are
kept running, this design is the cheapest, but takes the longest to
execute.
• A pilot light system, where a minimal duplicate system is prepared and
ready, but only the bare minimum services are up and running until a
failure. This approach is the next most expensive, but is quicker to return
to service than a cold restoration.
• A warm standby system, when a complete running environment is ready
to take over, but the resources are downsized, and expanded to full pro-
duction capacity only when needed. It is still more expensive than the
first two options, but is able to restore a minimal service level quickly.
• A hot standby system, where a complete, fully resourced duplicate envi-
ronment is ready to take over for the primary at all times. This is the
most expensive and most complex system to design, but enables the
shortest possible RTO.
High Availability
This is not actually a backup term, but the concept does overlap significantly
with disaster recovery. At its most basic, high availability is concerned with
designing and maintaining business solutions that must support very small
RTOs (typically measured in minutes or seconds), and RPOs as small as zero
(i.e., operational data must be current at all times, even during failures). The
line between hot standby designs and high availability implementations gets
blurry, as required RTOs and RPOs approach zero. Typically, a high availability
solution will include live, redundant synchronization of data, as well as a sepa-
rate implementation for longer term backup and archive. Consequently, these
implementations can be very expensive.
62 | THE DOPPLER | SUMMER 2018