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Reliability, Availability, and Maintainability

• Definition Reliability, Availability, and
  Maintainability (RAM or RMA) are system design
  attributes that have significant impacts on the
  sustainment or total Life Cycle Costs (LCC) of a
  developed system. Additionally, the RAM
  attributes impact the ability to perform the
  intended mission and affect overall mission
  success. The standard definition of Reliability
  is the probability of zero failures over a
  defined time interval (or mission), whereas
  Availability is defined as the percentage of time
  a system is considered ready to use when tasked.
  Maintainability is a measure of the ease and
  rapidity with which a system or equipment can be
  restored to operational status following a
  failure.
• Keywords availability, maintainability, RAM,
  reliability, RMA

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Reliability, Availability, and Maintainability

• MITRE SE Roles Expectations MITRE systems
  engineers (SEs) are expected to understand the
  purpose and role of Reliability, Availability,
  and Maintainability (RAM) in the acquisition
  process, where it occurs in systems development,
  and the benefits of employing it. MITRE systems
  engineers are also expected to understand and
  recommend when RAM is appropriate to a situation
  and if the process can be tailored to meet
  program needs. They are expected to understand
  the technical requirements for RAM as well as
  strategies and processes that encourage and
  facilitate active participation of end users and
  other stakeholders in the RAM process. They are
  expected to monitor and evaluate contractor RAM
  technical efforts and the acquisition program's
  overall RAM processes and recommend changes when
  warranted.

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Analysis of software availability/reliability
under the influence of hardware failures

• a new hardware-software reliability model is
  developed where lifetimes and repair times of the
  software subsystem have general system
  state-dependent distributions. The hardware
  subsystem constitutes an independent alternating
  renewal process having exponential up-times and
  general down-times. Multiple errors may be
  introduced or removed through repairs. The model
  is formulated as a multivariate stochastic
  process. To study the performance of the software
  subsystem under the influence of hardware
  failures, expressions of various time dependent
  performance measures are derived. Using the
  matrix Laguerre transform of U. Sumita (1984),
  corresponding computational procedures are also
  developed. A numerical example is given
  demonstrating the speed, accuracy, and stability
  of these procedures.

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Objectives

• To explain what is meant by a critical system
  where system failure can
• have severe human or economic consequence.
• To explain four dimensions of dependability -
  availability, reliability, safety
• and security.
• To explain that, to achieve dependability, you
  need to avoid mistakes,
• detect and remove errors and limit damage caused
  by failure

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Dependability

• Untrustworthy systems may be rejected
• by their users
• System failure costs may be very high
• It is very difficult to tune systems to make
• them more dependable
• It may be possible to compensate for
• poor performance
• Untrustworthy systems may cause loss of
• valuable information
• Dependability costs tend to increase
• exponentially as increasing levels of
• dependability are required
• There are two reasons for this
• The use of more expensive development
• techniques and hardware that are required
• to achieve the higher levels of
• dependability
• The increased testing and system
• validation that is required to convince the