In spite of the fact that Cloud Computing Environments (CCE) host many I/O intensive applications such as Web services, big data and virtual desktops, virtual machine monitors like Xen impose high overhead on CCEs' delivered performance hosting such applications. Studies have shown that hypervisors such as Xen favor compute intensive workloads while their performance for I/O intensive tasks is far from satisfactory. In this paper we present a new mechanism called cCluster to mitigate I/O processing delay in CCEs. To this end, cCluster classifies running virtual machines into I/O and computation VMs, and based on this classification, it dynamically classifies exiting physical cores into I/O and computation cores too. It then schedules I/O virtual CPUs (vCPU) on I/O cores and computation vCPUs on computation cores. Empirical results demonstrate that cCluster remarkably reduces the I/O response time and thus improves the network throughput.