Question

1. Assume that an NFS server contains a file /a/b and that an NFS client mounts

   the NFS server’s root directory in the location /x, so that the client can now name the file as /x/a/b. Further assume that this is the only client and that the

   client executes the following two commands:

   chdir /x/a
   rm b
   The REMOVE message from the client to the server gets through, and the server removes the file. Unfortunately, the response from the server to the client is lost and the client resends the message to remove the (now non-existent) file. The server receives the resent message. What happens next depends on the server implementation. Which of the following are correct statements?

   A. If the server maintains an in-memory reply cache in which it records all operations it previously executed, and there are no server failures, the server will return “OK”.
   B. If the server maintains an in-memory reply cache but the server has failed, restarted, and its reply cache is empty, both of the following responses are possible: the server may return “file not found” or “OK”.

   C. If the server is stateless, it will return “file not found”.
   D. Because REMOVE is an idempotent operation, any server implementation will return “OK”.

2. Do little bit of research on Apache Spark. What is it and how is it different from MapReduce? Compare their pros and cons.

Answer 1

The solution to the problem is

A. If the server maintains an in-memory reply cache in which it records all operations it previously executed, and there are no server failures, the server will return “OK”.

Explaination to above answer:

In NFS client and server architecture a lot of files are accessed and handled at once. There may be a scenario where a client may issue many system calls on a single file, each call converting to NFS operations. To keep track of each actions on a file NFS uses FILE HANDLES.

FILES HANDLES are assigned to clients and are unique identifier to a file. FILE HANDLES uniquely represent a file in NFS system.

So when REMOVE operation is performed on a file that is just deleted and response from server to client is lost. It will print OK message on client side beacause of server side caching.