Report Number: CSL-TR-73-62
Institution: Stanford University, Computer Systems Laboratory
Title: A highly efficient redundancy scheme: self-purging redundancy
Author: Losq, Jacques
Date: July 1975
Abstract: The goals of this paper are to present an efficient
redundancy scheme for highly reliable systems, to give a
method to compute the exact reliability of such schemes and
to compare this scheme with other redundancy schemes. This
redundancy scheme is self-purging redundancy; a scheme that
uses a threshold voter and that purges the failed modules.
Switches for self-purging systems are extremely simple: there
is no replacement of failed modules and module purging is
quite simply implemented. Because of switch simplicity, exact
reliability calculations are possible. The effects of switch
reliability are quantitatively examined. For short mission
times, switch reliability is the most important factor:
self-purging systems have a probability of failure several
times larger than the figure obtained when switches are
assumed to be perfect. The influence of the relative
frequency of the diverse types of failures (permanent,
intermittent, stuck-at,...) are also investigated.
Reliability functions, mission time improvements and switch
efficiency are displayed. Self-purging systems are compared
with ot her redundant systems, like hybrid or NMR, for their
relative merits in reliability gain, simplicity, cost and
confidence in the reliability estimation. The high confidence
in the reliability evaluation of self-purging systems makes
them a standard for the validation of several models that
have been proposed to take into account switch reliability.
The accuracy of models using coverage factors can be
evaluated that way.