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\title{Basics of Information Systems}
\author{Winter Semester 2022--23}
\date{For discussion on Wednesday, January 11, 2022}
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\begin{enumerate}
\item Soft and hard links are often used for convenience purposes when
structuring file data.  To avoid unexpected behavior, it is important
to understand their behavior, in particular the conceptual differences
between soft and hard links.  Answer each of the following questions
for soft and for hard links separately.
\begin{enumerate}
\item Suppose you set a link named \texttt{linktofile} to a file named
\texttt{fileA}.  Then you delete \texttt{fileA}.  What happens?  Is
the data gone?  If not, how do you access it?

\item Suppose you set a link named \texttt{linktofile} to a file named
\texttt{fileA}.  Then you delete \texttt{linktofile}.  What happens?  Is
the data gone?  If not, how do you access it?

\item Can you determine if a file is being linked to?  How?  (There is
no need to describe precise Unix/Windows commands, a conceptual answer
suffices.)

\item Suppose you write a program to copy (a part of a) file system to
a backup location and to restore the data from backup if necessary.
What may go wrong if your data includes hard or soft linked files?

\item You are about to modify a file that is being linked to.  Because
you are unsure about the modification, you want to keep an old copy
around.  How to you proceed?  What do you have to be aware of?

\item Can you link to a directory?  What can possibly go wrong?

\item What is faster -- file access via a hard link or via a soft
link?

\end{enumerate}

\item RAID arrays are often used to increase storage capacity and/or
reliability.  Some of the important operational modes, called
\emph{RAID levels}, are RAID-0, RAID-1, RAID-5.  Answer the following
questions, comparing these three RAID levels.

\begin{enumerate}
\item Which RAID levels improve the data transfer rate for writes?
\item Which RAID levels improve reliability?
\item Which RAID levels reduce reliability?  By how much?
\item How many drives are allowed to fail in each RAID level?
\item Name at least two reasons why RAID is not a backup solution.
\item How much capacity does each RAID level provide if a single drive
has storage capacity $C$?
\end{enumerate}



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