$($a$)$ State two differences between public clouds and traditional data centers. $($b$)$ Explain how Spark improves the performance of Dijkstra's algorithm in MapReduce. $($c$)$ BigTable keeps an SSTable immutable. State one advantage and one disadvantage of this design choice. $($d$)$ Suppose that Amazon Dynamo stores object i in node j based on consistent hashing using $3-$way replication, where i $=1,2,3,.,100$ and j $=10,20,30,...,100($where i and j represent the object key and the node key, respectively$).$ Now, node $65$ joins the system. Explain how the system relocates the objects and their replicas. $($e$)$ Dropbox uses server$-$side deduplication instead of client$-$side deduplication. State one advantage and one disadvantage. $($f$)$ One way to reduce tail latency is to send tied requests. However, the medium latency of requests can increase. State two possible reasons.