  In this paper, we show that performance of the virtualized cluster servers
could be improved through intelligent decision over migration time of Virtual
Machines across heterogeneous physical nodes of a cluster server. The cluster
serves a variety range of services from Web Service to File Service. Some of
them are CPU-Intensive while others are RAM-Intensive and so on. Virtualization
has many advantages such as less hardware cost, cooling cost, more
manageability. One of the key benefits is better load balancing by using of VM
migration between hosts. To migrate, we must know which virtual machine needs
to be migrated and when this relocation has to be done and, moreover, which
host must be destined. To relocate VMs from overloaded servers to underloaded
ones, we need to sort nodes from the highest volume to the lowest. There are
some models to finding the most overloaded node, but they have some
shortcomings. The focus of this paper is to present a new method to migrate VMs
between cluster nodes using TOPSIS algorithm - one of the most efficient Multi
Criteria Decision Making techniques- to make more effective decision over whole
active servers of the Cluster and find the most loaded serversTo evaluate the
performance improvement resulted from this model, we used cluster Response time
and Unbalanced Factor.
