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Figure 4:
The steps of duplication process for Protocols 3 and 4.
![\begin{figure}\centering \centerline{\hbox{\epsfig{figure=NewFigures/epvfsp3.eps, width=3in}}} \end{figure}](img27.png) |
In this protocol, the duplication task is assigned to the client,
as shown in Figure 4. After fetching, the client can
write to the primary and backup servers simultaneously. The
duplication process is regarded as successful after receiving at
least one acknowledgment among each pair of mirrored servers.
Obviously, there is a potential problem if the slower server in
the pair fails before acknowledgment. This problem is similar, but
not identical to that in Protocol 1.
Yifeng Zhu
2003-10-16