CS E6998-10. Advanced Topics in Network Storage Systems February 10, 2004 Quiz #1 Name: ID#: Give short answers to the following questions: (10 points) 1. HP AutoRAID is a hierarchical storage system. Which are the two storage hierarchies and what are the tradeoffs between them? How is migration triggered between the two levels? RAID1 (mirrored) and RAID5 (parity) (4 points) Space tradeoff: RAID5 more space-efficient (2 points) RAID1 replicates each data block RAID5 uses only one parity block per stripe Performance tradeoff: RAID1 performs small writes faster (2 points) RAID1 writes to replicas RAID5 has to read old parity block in order to recalculate Migration from RAID1 to RAID5 is triggered by a least-recently written protocol, to ensure free space in the RAID1 hierarachy (1 point) Migration from RAID5 to RAID1 takes place when data that is in RAID5 are written (1 point) (10 points) 2. NFS was designed as a stateless protocol. What is the primary benefit of this design choice? Rapid recovery (10 points) (10 points) 3. One of AFS's design goals is scalability. Mention two design aspects of AFS that help achieve that goal. Client caching (5 points) Multiple servers (5 points) (10 points) 4. HA-NFS can survive and recover from disk, network, and server failures. Briefly describe the process of "take-over" (aka "failover") from a server failure. Surviving server: 1. Brings file systems of failed server to consistent state by running its logs. (4 points) 2. Retrieves failed server's reply cache entries and inserts into its own log. (3 points) 3. Start impersonating failed server by changing the IP address and MAC address of its secondary network interface to those of the failed server's primary interface. (3 points)