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Availability is defined in this paper to be the fraction of time
when a system is operational. More precisely, it is defined as
follows.
![\begin{displaymath}
Availability = \frac{MTTF}{MTTF + MTTR}
\end{displaymath}](img139.png) |
(14) |
Figure 16 and Figure 17
give the availability comparisons between the four duplication
protocols and PVFS within the same scenarios as the reliability
analysis. While the availability of PVFS is only 0.91, 0.85 and
0.73 in the three server configurations, respectively, the
availability of CEFT-PVFS with four duplication protocols are all
above 0.99. Similarly with the reliability comparisons, Protocol 2
and 4 achieve a better availability than Protocol 1 and 3.
Figure 16:
Availability comparison of CEFT-PVFS and PVFS
![\begin{figure}\epsfig{figure = blackfigures/AvailabilityBar.eps, width=3in} \end{figure}](img140.png) |
Figure 17:
Availability comparison of four duplication protocols
![\begin{figure}\par\epsfig{figure = blackfigures/Availability2Bar.eps, width=3in} \end{figure}](img141.png) |
Yifeng Zhu
2003-10-16