Chapter 7

1. A file is replicated on 6 servers. List all the combinations of read quorum and write quorum that are permitted by the voting algorithm.
2. What kind of consistency would you use to implement an electronic stock market? Explain your answer
3. Linearizability assumes the existence of a global clock. However, with strict consistency we showed that such an assumption is not realistic for most distributed systems. Can linearizability be implemented for physically distributed data stores?

Chapter 8

4. Suppose we have a system with 99.9996% availability, how much downtime a year can it have?
5. Write the reliability expression R_system(t) of the following series/parallel system, assuming that each of the five modules has a reliability of R(t).

Chapter 9

6. Devise a simple authentication protocol using signatures in a public-key crypto-system.
7. How are ACLs implemented in a UNIX file system?

Chapter 11

8. Explain whether or not NFS is to be considered a distributed file system.
9. In UNIX-based operating systems, opening a file using a file handle can be done only in the kernel. Give a possible implementation of an NFS file handle for a user-level NFS server for a UNIX system.
10. Does NFS implement entry consistency?