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RAS Technology is an operational characteristic of
a today's computer systems and is based on the three interrelated
performance elements of Reliability, Availability, and Serviceability.
Reliability is the measure over time of the consistency with which a
system successfully performs its computing and communication services.
Serviceability is the measure over time of the ease with which a degraded
system can be restored to its full operating posture. Availability is
the measure over time of the percentage of the time during which the
system provides specified services to its users. The measurement and
characteristics of systems performance with regard to these three interrelated
performance elements can be referred to as RAS for the system RAS.:
• Reliability is the probability that components, parts
and the systems they comprise will perform their required functions
for a period of time without failure in the specified environments
with a degree of acceptable confidence. The measurement of systems
reliability does not account for any repair action that may take place,
and is intended only to account for the duration that is required for
the system to fail while it is in operation. Nor does the measure of
a systems Reliability reflect the time required or taken to restore
the unit to operations.
• Availability is the probability that the system will be able to
conduct its normal services function when it is called upon, given that a failure
not occurred or the system has undergone a repair action. The objective is to
provide a systems that is totally 100% available when considering both reliability
and serviceability measures.
• Serviceability is measurement of how easily and quickly a repair
can be accomplished considering the modularity or the system design, the duality
of components, the ability to mirror and restore data, and the availability of
hot swap components.
System Availability and Reliability seem closely related, but they are
fact quite different. Availability is normally measured as the percent
of time that a system is ready for access and use by the user. A variety
of factors can adversely impact this measurement ranging from planned downtime
for preventive maintenance, to a catastrophic failure induced by environmental
disaster or malicious action. The ultimate goal of high availability system
solutions is to minimize this downtime by component redundancy, alternate
processing and data storage paths, and by developing a Serviceability process
that is quick and effective based on just how much downtime can be tolerated.
On the one hand a systems availability plan could encompass a restoration
of operations in a matter of hours or days, while on the other hand the
need may be for 100% continuous availability. |
