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\begin{center}
Summary and Conclusions
\end{center}
\begin{itemize}
\item We have suggested disk subsystem performance enhancement
by (virtual) cylinder remapping.  
\item We measured workload
on a real UNIX system and found that disk accesses could be reasonably
characterized by a first order Markov model.  
\item We used simulated
annealing to find a permutation of the (virtual)
cylinders that reduced expected seek distance.
\item We installed this permutation in a real system 
and found a 25.6\% reduction in
mean service time when compared to the original (unmapped)
arrangement.
\end{itemize}

We observe:
\begin{itemize}
\item Disk remapping provides an opportunity to optimize performance for
multiple workloads. 
\item A fault tolerant system might maintain multiple copies 
with different mappings.
\item The realized 25.6\% improvement may
be conservative: 
\begin{itemize}
\item The distribution of requests across the virtual cylinders
happened to be highly non-uniform.  
\item The annealing algorithm strives to minimize average
seek distance, but our interest is average seek time.
\end{itemize}
\end{itemize}
