Redpaper - IBM Redbooks
Redpaper - IBM Redbooks
Redpaper - IBM Redbooks
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1.1 Project overview<br />
This paper explores the architecture and explains the tasks necessary to build a<br />
high availability environment for Message Broker on z/OS. Remember that the<br />
Message Broker high availability environment is necessary for the business<br />
applications that it serves and not for itself. Today’s business critical applications<br />
often demand a high degree of availability, and the z/OS system administrator<br />
must exploit Parallel Sysplex technology to provide continuous service levels<br />
during system outages, planned or otherwise.<br />
1.1.1 Availability levels<br />
There are several ways to describe the degree of availability that a system<br />
requires. The availability of a system can be expressed as a number of nines or<br />
by using different terms.<br />
The number of nines term represents the percentage of time for which the<br />
system is available. Three nines means that it is available 99.9% of the time; five<br />
nines means that it is available 99.999% of the time. These numbers become<br />
much more significant when you look at these figures in terms of downtime over<br />
a fixed period. For example, over a period of one year, a system with 99.9%<br />
availability would have 8.75 hours of downtime, while a system with 99.999%<br />
availability would be down for just 315 seconds.<br />
The following terms are also used to describe availability:<br />
► Continuous availability: This term describes a system that experiences no<br />
discernible downtime, where neither scheduled nor unscheduled outages<br />
occur. A continuously available system detects the error and immediately<br />
provides an alternative component that is already ready to go. Also, this<br />
system should support the scheduling of planned maintenance by allowing<br />
workload to be transparently transferred away from the components or<br />
subsystems that are the subject of the maintenance activity. Although<br />
continuous availability seems difficult to achieve, it is possible to obtain such<br />
availability by combining hardware, software, and operational procedures that<br />
can mask outages from the user so that the user does not perceive that a<br />
system outage occurs.<br />
► Continuous operation: This term describes a system that experiences no<br />
discernible downtime due to scheduled outages. However, this system's<br />
availability will not be as high as it would be with a continuously available<br />
system because it may suffer unplanned outages.<br />
► High availability (HA): This term describes a system that can detect a single<br />
failure and react to it automatically within a matter of a few minutes at most.<br />
2 High Availability z/OS Solutions for WebSphere Business Integration Message Broker V5
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