Improving Serviceability for Virtual Clusters in Bandwidth-Constrained Datacenters

Virtual cluster is a useful resource descriptive model, in terms of virtual machines (VMs) and link bandwidth, for many data center applications that require predictable performance. Bandwidth-constrained data centers often use reservation schemes to statically allocate underlying physical resources to virtual clusters. However, due to highly varying workloads, existing reservation schemes may place VMs improperly, causing a waste of bandwidth reservation and eventually leading to rejecting new virtual cluster requests even the VM capacity is sufficient. In this paper, we propose a mechanism to detect and rectify such bandwidth-wasting VM placements via VM reshuffling. To compute a new VM placement accommodating new requests as many as possible, we formulate an optimization problem, with the objective of minimizing the reservations of limited bandwidth. The problem is NP-hard. We propose two efficient algorithms for a practical special case and the general case of the problem respectively. To evaluate our mechanism, we conduct simulation with the settings close to real data center environments. The results show that our mechanism with VM reshuffling achieves a significant reduction in rejecting virtual cluster requests and increases data center throughput over various high loads.