Availability Analysis

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Availability Analysis

Availability is defined in this paper to be the fraction of time when a system is operational. More precisely, it is defined as follows.

$\begin{displaymath} Availability = \frac{MTTF}{MTTF + MTTR} \end{displaymath}$

(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
$\begin{figure}\epsfig{figure = blackfigures/AvailabilityBar.eps, width=3in} \end{figure}$

**Figure 17:** Availability comparison of four duplication protocols
$\begin{figure}\par\epsfig{figure = blackfigures/Availability2Bar.eps, width=3in} \end{figure}$

Yifeng Zhu 2003-10-16