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Added quiz on persistence section (filesystems).
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| --- | ||
| course: 'CSCI 3431: Operating Systems' | ||
| qznumber: 4 | ||
| qzdate: '2 December 2014' | ||
| qztitle: 'Persistence' | ||
| instructions: | | ||
| Answer each of the following questions in complete sentences. | ||
| Take note of point values. | ||
| question: | ||
|
|
||
| - keywords: filesystem, | ||
| points: 12 | ||
| space: 1.5 | ||
| text: | | ||
| You attend a hackathon based on the recent opening of CERN data. | ||
| When you attempt to quick sort the data you unleash the true powers of the newly discovered $\Xi_b^-$ baryons, which transfer your conciousness into your computer! | ||
| In the process of this unbelievable human-to-computer transfer you corrupt the filesystem. | ||
| Your only hope of survival is to fix the following filesystem states. | ||
| Explain whether you can repair the state and how, or what you should do to protect the system from harm (reading garbage data). \newline | ||
| \textbf{Note:} Every data block has data, you have to determine (and indicate) if it is garbage or not. | ||
| \begin{table}[h] | ||
| \centering | ||
| \scalebox{1.0}{% | ||
| \begin{tabular}{|l|c|c|c|c|} | ||
| \hline | ||
| inodes bitmap & 1 & 1 & 1 & 0 \\ \hline | ||
| inodes & {[}d a:0 r:4{]} & {[}d a:1 r:2{]} & {[}f a:2 r:1{]} & {[}{]} \\ \hline | ||
| data bitmap & 1 & 0 & 0 & 1 \\ \hline | ||
| data & {[}(.,0) (..,0) (a,1) (b,2){]} & {[}(.,1) (..,0){]} & {[}x{]} & {[}y{]} \\ \hline | ||
| \end{tabular} | ||
| } | ||
| \end{table} | ||
| \vspace{1.5in} | ||
| \begin{table}[h] | ||
| \centering | ||
| \scalebox{1.0}{% | ||
| \begin{tabular}{|l|c|c|c|c|} | ||
| \hline | ||
| inodes bitmap & 1 & 0 & 1 & 0 \\ \hline | ||
| inodes & {[}d a:0 r:4{]} & {[}{]} & {[}f a:3 r:1{]} & {[}{]} \\ \hline | ||
| data bitmap & 1 & 0 & 1 & 0 \\ \hline | ||
| data & {[}(.,0) (..,0) (c,2) (d,4){]} & {[}(.,1) (..,0){]} & {[}x{]} & {[}y{]} \\ \hline | ||
| \end{tabular} | ||
| } | ||
| \end{table} | ||
| \vspace{1.5in} | ||
| \begin{table}[h] | ||
| \centering | ||
| \scalebox{1.0}{% | ||
| \begin{tabular}{|l|c|c|c|c|} | ||
| \hline | ||
| inodes bitmap & 0 & 0 & 0 & 0 \\ \hline | ||
| inodes & {[}d a:0 r:4{]} & {[}f a:1 r:2{]} & {[}f a:2 r:1{]} & {[}{]} \\ \hline | ||
| data bitmap & 1 & 1 & 0 & 0 \\ \hline | ||
| data & {[}(.,0) (..,0) (e,1) (g,2){]} & {[}z{]} & {[}x{]} & {[}y{]} \\ \hline | ||
| \end{tabular} | ||
| } | ||
| \end{table} | ||
| \newpage | ||
| - keywords: filesystem, | ||
| points: 4 | ||
| space: 2 | ||
| text: | | ||
| A hard link is a directory entry that associates a name with a file on the filesystem. | ||
| A symbolic link is a special file that contains a reference to another file or directory in the form of a path. | ||
| The target is independent of the symbolic link. \newline | ||
| Our filesystem starts in the following state: | ||
| \begin{table}[h] | ||
| \centering | ||
| \scalebox{1.0}{% | ||
| \begin{tabular}{|l|c|c|c|c|c|c|c|c|} | ||
| \hline | ||
| inodes bitmap & 1 & 1 & 1 & 0 & 0 & 0 & 0 & 0 \\ \hline | ||
| inodes & {[}d a:0 r:4{]} & {[}d a:1 r:2{]} & {[}f a:2 r:1{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} \\ \hline | ||
| data bitmap & 1 & 1 & 0 & 0 & 0 & 0 & 0 & 0 \\ \hline | ||
| data & {[}(.,0) (..,0) (g,1) (q,2){]} & {[}(.,1) (..,0){]} & {[}a{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} \\ \hline | ||
| \end{tabular} | ||
| } | ||
| \end{table} | ||
| Determine if the following state represents the filesystem after the creation of a hard link or a symbolic link. | ||
| Explain your answer. | ||
| \begin{table}[h] | ||
| \centering | ||
| \scalebox{1.0}{% | ||
| \begin{tabular}{|l|c|c|c|c|c|c|c|c|} | ||
| \hline | ||
| inodes bitmap & 1 & 1 & 1 & 0 & 0 & 0 & 0 & 0 \\ \hline | ||
| inodes & {[}d a:0 r:4{]} & {[}d a:1 r:2{]} & {[}f a:2 r:2{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} \\ \hline | ||
| data bitmap & 1 & 1 & 0 & 0 & 0 & 0 & 0 & 0 \\ \hline | ||
| data & {[}(.,0) (..,0) (g,1) (q,2){]} & {[}(.,1) (..,0) (p,2){]} & {[}a{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} & {[}{]} \\ \hline | ||
| \end{tabular} | ||
| } | ||
| \end{table} | ||
| - keywords: IO | ||
| points: 3 | ||
| space: 2 | ||
| text: | | ||
| There are two common methods of low level device interaction used today: IO instructions and Memory mapped IO, explain both. \newline | ||
| Choose one and name a benefit or negative of that approach. | ||
| \newpage | ||
| - keywords: IO | ||
| points: 3 | ||
| space: 2 | ||
| text: | | ||
| What does DMA stand for? What does a DMA controller do? Why would we want our hardware and OS to support one? | ||
| - keywords: filesystem | ||
| points: 6 | ||
| space: 3 | ||
| text: | | ||
| We discussed two different techniques to reference data blocks on a filesystem: multi-level indexing and extents. | ||
| Describe both and compare their benefits under different conditions. | ||
| - keywords: filesystem | ||
| points: 3 | ||
| space: 2 | ||
| text: | | ||
| You are designing a video editing system that will store multi gigabyte files. \newline | ||
| The old unix beard at the office says to use a 4 kilobyte block size on the filesystem because it's a standard. \newline | ||
| What do you do? | ||
| - keywords: filesystem | ||
| points: 1 | ||
| space: 1 | ||
| text: | | ||
| Bonus scenario! \newline | ||
| The unix beard now respects you for your intelligent input, do you dare make a comment on his use of the word kilobyte? | ||
| What might the International Electrotechnical Commission think of this confusing use of SI prefixes? | ||
| ... |