1. 1 Discussion Class 8 The Google File System

2. 2 Discussion Classes Format: Question Ask a member of the class to answer. Provide opportunity for others to comment. When answering: Stand up. Give your name. Make sure that the TA hears it. Speak clearly so that all the class can hear. Suggestions: Do not be shy at presenting partial answers. Differing viewpoints are welcome.

3. 3 Question 1: Reading a Paper -- Jargon Define the following terms: POSIX Linux buffer cache Atomic record Namespace management

4. 4 Question 2: File System (a)What is the purpose of a file system, such as the Google File System? (b)How does a file system interact with the other parts of a computer system? (c)Why does Google not use the standard Linux file system? (d)Why does Google not use the Posix API? (e)What does Google lose by having its own file system?

5. 5 Question 3: Interface In addition to the standard operations of create, delete, open, close, read, and write, the Google File System has two special operations: snapshot record append (a) What do these two operations do? (b) Give examples of applications that these operations are designed to support.

6. 6 Question 4: Master Servers The Google File System uses clusters each consisting of one master server and several chunk servers. (a)What role does each play? (b)What are the advantages of this architecture? (c)What precautions are taken to prevent the master server becoming a bottleneck?

7. 7 Question 5: Performance Discuss these three performance graphs.

8. 8 Question 6: Recovery Experiment The paper describes two recovery experiments on a cluster containing 15,000-16,000 chunks with 600-660 GB of data. (a)One chunk server was killed. Recovery time was 23 minutes. Describe the process. (b)Two chunk server were killed. Explain how the recovery process was changed. (c)Suppose that the master server had been killed. How would the recovery have taken place?

9. 9 Question 7: Consistency Model (a)What is a consistency model? (b)How does the consistency model used by the Google File System differ from the model that might be used by a general purpose file system? (c)How does the file system guarantee correctness of the namespace? (d)Explain what happens, from a consistency viewpoint, when an application attempts to append to a file.