There are two forms of automated migration provided by Windows Server 2008 R2 Hyper-V: Quick Migration and Live Migration. These migration processes can be used to increase service availability for planned and unplanned downtime. Although both technologies achieve the same thing—moving virtual servers between Hyper-V hosts—they use different methods and mechanisms to achieve it. Both require at least two Hyper-V host servers in a cluster, attached to the same shared storage system. Usually, the shared storage is an iSCSI or Fibre Channel storage area network (SAN).
Quick Migration provides a way to quickly move a virtual machine from one host server to another with a small amount of downtime.
In a Quick Migration, the guest virtual machine is suspended on one host and resumed on another host. This operation happens in the time it takes to transfer the active memory of the virtual machine over the network from the first host to the second host. For a host with 8GB of RAM, this might take about two minutes using a 1GB iSCSI connection.
Quick Migration was the fastest migration available for Windows Server 2008 Hyper-V. Microsoft made considerable investments in Hyper-V migration technologies, trying to reduce the time required to migrate virtual machines between Hyper-V hosts. The result was Live Migration, which has the same hardware requirements as Quick Migration, but with a near instantaneous failover time.
Since the release of Hyper-V V1 with Windows Server 2008, the number-one mostrequested feature by customers is the ability to migrate running virtual machines between hosts, with no downtime. VMware’s VMotion has been able to do this for some time. Finally, with Windows Server 2008 R2, it can be done natively with Hyper-V for no extra cost. This makes it a compelling reason to move to Hyper-V.
Live Migration uses failover clustering. The quorum model used for your cluster will depend on the number of Hyper-V nodes in your cluster. In this example, we will use two Hyper-V nodes in a Node and Disk Majority Cluster configuration. There will be one shared storage LUN used as the cluster quorum disk and another used as the Cluster Shared Volume (CSV) disk.
If there is only one shared storage LUN available to the nodes when the cluster is formed, Windows will allocate that LUN as the cluster quorum disk and it will not be available to be used as a CSV disk.
Source of Information : Sams - Windows Server 2008 R2 Unleashed