INFORMATION AVAILABILITY
Achieving Continuous
Availability with
A transaction can be sent to any node
and will be processed in the same way as
it would be at any other node. Should a
fault occur that causes a node to fail, all
that needs to be done is to reroute transactions to a surviving node. Recovery can
be accomplished in seconds to subseconds.
Active/Active Networks
Dr. BILL HIGHLEYMAN
Amajor UK bank has experi- enced no major system out- ages in its ATM network for 15 years. How has it achieved this
remarkable availability? Through the use
of an active/active network architecture.
Many enterprises in the financial, telecommunications, health, transportation,
gaming, and other industries have reported
similar experiences. Let’s look at how
these continuously-available active/active
networks work along with their advantages and pitfalls.
What Do We Mean by
Continuous Availability?
First of all, we must explain what we
mean by “continuous availability.” A
continuously-available system is one that
provides expected services to its users at
all times, no matter what. No single failure
will take it down. It never has to be taken
out of service for planned maintenance
such as upgrades. It continues to provide
service even if a data center blows up.
Clearly, there will be hardware faults,
software bugs, operator errors, power
failures, hurricanes, floods, and terrorist
attacks. No system is immune to outages.
But if the recovery from an outage is so
fast that no one notices, continuous availability has been achieved. In other words,
“let it fail but fix it fast.” That is the philosophy behind active/active systems.
The Active/Active Architecture
Database Replication
