Testing Replica Selection Policies in a Pan-European Grid VO

In a typical grid environment, replicas are spread over storage hosts, so as to increase availability and reduce files transfer times. Generally, the grid middleware lets users choose the storage host that will be serving the replica. However, having users able to choose could adversely affect network conditions and increase transfer times. This paper proposes two replica selection policies that choose one among the storage hosts holding a requested replica. The selection policies try to minimise file transfer time by extracting the least loaded host or the closest among unloaded hosts. It is shown that overall performances for transferring replicas depend on network topology, latency and bandwidth of links, and load of storage hosts and links.