\chapter{Data Reduction Software}

\section{Operational Phases}

The data reduction software supports three models:

\begin{itemize}
\item {\bf offline} processing: performed after the recording has finished
\item {\bf simultaneous} processing: performed during the recording
\item {\bf diskless} processing: as above, but completely in memory
\end{itemize}

\subsection{Offline Data Reduction}

The data reduction software operates only on data files stored on
local disk space, and only after the recording has completed.  After
the observations have been completed, the data files from each Primary
node will be farmed out to the Secondary nodes.  After each file has
been copied, an entry will be added to the log file that is monitored
by the Configuration and Scheduling software, which will attend to the
data reduction as described in Chapter 6.

\subsection{Simultaneous Data Reduction}

The data reduction software runs during the observation.  In this
mode, data are sent directly to Secondary nodes and written to disk.
As before, an entry will be made in a log file and the Configuration
and Scheduling software will coordinate the data reduction.

\subsection{Diskless Data Reduction}

The data reduction software is able to keep up completely with the
flow of data on the Primary nodes.  In this case, the data is never
written to disk, and {\tt dspsr} operates as a Read Client directly
connected to the Data Block.  Another Read Client may be written that
will farm data reduction tasks to a grid computing facility.  In this
case, the data reduction Read Client will have to incorporate the
Configuration and Scheduling tasks.

