Homework 4

Total points 10

Question 1A Unix-style file system read does not specify which offset in the file to start reading from. This is because this file system uses: 1 point

• One read-write pointer for each file descriptor, which is automatically advanced upon a read

• A read-write pointer for the system, which is automatically advanced upon a read

• One read-write pointer for each file, which is automatically advanced upon a read

• One read-write pointer for each file descriptor, which can be advanced only via the lseek call

SOLUTION-One read-write pointer for each file descriptor, which is automatically advanced upon a read

Question 2 A distributed file system does not typically use read-write pointers. The reasons for this DO NOT include: 1 point

• Repeatability of operations by clients without any side effects

• Idempotence of operations

• Read-write pointers are buggy

• Stateless servers

SOLUTION-Read-write pointers are buggy

Question 3

Which of the following is FALSE about the NFS file system? 1 point

• If a file is remote, the v-node will point to the remote NFS server or remote block/file.

• NFS allows mounting of directories.

• Because it is a distributed file system, it does not support read-write pointers for end processes.

• If a file is local, the v-node points to the local i-node.

SOLUTION-Because it is a distributed file system, it does not support read-write pointers for end processes.

Question 4 Which of the following is FALSE about AFS? 1 point

• When a file is accessed, the Venus client fetches the entire file.

• All file accesses by a process are served from the locally cached copy of the file at the Venus client.

• The Venus cache for a file is treated as a write-back (or delayed write) cache.

• The Venus cache for a file is treated as a write-through cache.

SOLUTION-The Venus cache for a file is treated as a write-through cache.

Question 5 In a distributed shared memory system, the best value to set a page size to should be: 1 point

• At or slightly larger than locality of interest

• Much larger than locality of interest

• Very large

• Smaller than locality of interest

SOLUTION-At or slightly larger than locality of interest

Question 6 Which of the following activities consumes most energy at a sensor mote? 1 point

• None, because all activities use the same energy as there is only one battery.

• Transmitting messages

• Executing instructions

• Sitting idle

SOLUTION-Transmitting messages

Question 7

In an NFS system, the freshness interval is set to 30 s. At time 10am:12min:25s, a client process with pid 356 accesses a locally cached copy of a file block, for which the client stores a last-modified timestamp of 10am:11min:35s, and the file block was last validated by the client at 10am:12min:3s. At the server, the last-modified timestamp of the file block is 10am:12min:4s. Then, the NFS client will: 1 point

• Fetch the file block from the server

• Serve the file block from the locally cached copy at the client

• This situation cannot arise.

• Fetch the server’s last-modified timestamp but not fetch the file block from the server

SOLUTION-Serve the file block from the locally cached copy at the client

Question 8 In an NFS system, the freshness interval is set to 3 s. At time 10am:12min:25s, a client process with pid 356 accesses a locally cached copy of a file block, for which the client stores a last-modified timestamp of 10am:11min:35s, and the file block was last validated by the client at 10am:12min:3s. At the server, the last-modified timestamp of the file block is 10am:12min:4s. Then, the NFS client will: 1 point

• Serve the file block from the locally cached copy at the client

• Fetch the server’s last-modified timestamp but not fetch the file block from the server

• Fetch the file block from the server

• This situation cannot arise.

SOLUTION-Fetch the file block from the server

Question 9A distributed shared memory system, using the invalidate approach, contains 4 processes P1 through P4. Currently, a page P is stored in read mode at processes P2 and P4, and P4 is the owner. A read from P1 will result in: 1 point

• P2 and P4's copies both are invalidated

• P1 fetching a copy of the page from either P2 or P4, and P4 remains the owner

• None of these options

• P1 reading the page P from its local cache

SOLUTION-P1 fetching a copy of the page from either P2 or P4, and P4 remains the owner

Question 10 A distributed shared memory system, using the invalidate approach, contains 4 processes P1 through P4. Currently, a page P is stored in read mode at processes P2 and P4, and P4 is the owner. A write from P3 will result in: 1 point

• P3 fetching a copy of the page from either P2 or P4, and then P3 can write P while P2 and P4 are reading P

• None of these options

• P3 will be given access only in read mode until P2 and P4 are done with their reads

• P3 invalidating the copies of P at P2 and P4, P3 fetching page P from P2 or P4, and then P3 becoming owner of P in write mode

SOLUTION-P3 invalidating the copies of P at P2 and P4, P3 fetching page P from P2 or P4, and then P3 becoming owner of P in write mode