The program {\tt cta-taped} is a daemon managing the tape drive and transferring data from tape to drive. The daemon is split in two levels of processes: the daemon process, which is a single threaded sub-process manager, which does not have any external connectivity. The sub-processes can be multi-threaded, and implement external connectivity. Two types of sub-processes implement different kinds of functionality.
The program {\tt cta-taped} is a daemon managing the tape drive and transferring data from tape to drive. The daemon has
two levels of processes:
\begin{description}
\item[The Daemon Process:] a single threaded sub-process manager which does not have any external connectivity. The
Daemon Process is very simple and has a long lifetime (in the order of months).
\item[Sub-processes:] implement external connectivity. Sub-processes can be multi-threaded. They have a short lifetime
with regular restarts, to limit the consequences of memory leaks or other potential bugs in third-party tape libraries.
\end{description}
There are several types of Sub-process. The main Sub-process is the drive sub-process (see below).
\begin{alertbox}
Other possible sub-processes:
\begin{itemize}
\item Labelling process?
\item Drive cleaning process?
\item Verification process? Perhaps not necessary as a read-only Drive process could do the job?
\end{itemize}
Are these part of the Drive sub-process or are they separate processes launched by the Drive sub-process?
\end{alertbox}
\clearpage
\section{Drive sub-process}
The main sub-process is the drive sub-process. One such sub-process will be launched per drive in the tape server. The drive process executes one mount and then exits. The daemon then restarts a new instance of it, passing the previous instances exit status. Based on this status of the previous run, the session could either become a cleaning session, where any potentially still mounted tape is removed from the drive, or start scheduling. Scheduling can lead to archive, retrieve or label sessions.
The tape session types and state changes are shown in figure \ref{statediag}.
One Drive sub-process is launched per drive in the tape server. The Drive sub-process executes one mount and then exits.
The daemon then restarts a new Drive sub-process instance, passing in the previous instances' exit status. Based on this
status from the previous run, the session could become either:
\begin{description}
\item[A Cleanup Session:] any potentially still-mounted tape is removed from the drive, or
\item[A Scheduling Session:] Scheduling can lead to Archive, Retrieve or Labelling sessions.
\end{description}
The tape session types and state changes are shown in Figure~\ref{statediag}.
