12.0 High Availability under Linux
This chapter contains a short overview of the key concepts and tools from
the area of high availability under Linux. It also offers suggested further
reading for all the topics mentioned.
High availability describes systems that can mask certain malfunctions—in particular, the failure of individual computers—so
the service can be made available to the user again after only a short
downtime. Hardware and software are carefully coordinated and laid out for
redundancy, enabling an automatic switch to the other components in the
event of a malfunction. High availability differs from error
tolerance
because the service is temporarily unavailable for the
short service switchover phase, which can be noticed in delays
or short losses in connection.
A high availability system particularly means when the
overall availability of the service is between 99.999 percent and
99.99999 percent. This
corresponds to a downtime of between five minutes and three seconds over an entire
year. The most important factor is not just the software and hardware side,
but, primarily, well-conceived system administration with well-documented
and understandable processes for minimizing faults. In every case, it
involves weighing risks and costs. Different requirements and
solutions may be appropriate, depending on the application scenario. Your
Novell partner will be happy to advise you.
