Reliable Partial Replication of Contents in Web Clusters: Getting Storage without losing Reliability

Traditionally, distributed Web servers have used two strategies for allocating files on server nodes: full replication and full distribution. While full replication provides a highly reliable solution, it limits storage capacity to the capacity of the smallest node. On the other hand, full distribution provides higher storage capacity at the cost of lower reliability. A hybrid solution is partial replication where every file is allocated to a small number of nodes. The most promising architecture for a partial replication strategy is the Web cluster architecture. However, Web clusters present a big flaw from reliability perspective as they contain a single point of failure. To correct this flaw, in this paper we present a modified architecture: the Web cluster with distributed Web switch. Reliability of Web clusters is evaluated for different replication strategies. System evaluations show that our proposal leads to a highly reliable solution with high scalability.