Performing a Live Migration

The virtual machine runs on one of the cluster nodes, known as the owner. When a Live Migration is performed, multiple steps are performed. These steps can be broken down into three stages: preflight migration, virtual machine transfer, and final transfer/startup of the virtual machine.

The first step in Live Migration occurs on the source node (where the virtual machine is currently running) and the target node (where the virtual machine will be moved) to ensure that migration can, in fact, occur successfully.

The detailed steps of Live Migration are as follows:
1. Identify the source and destination machines.

2. Establish a network connection between the two nodes.

3. The preflight stage begins. Check if the various resources available are compatible between the source and destination nodes:
. Are the processors using similar architecture? (For example, a virtual machine running on an AMD node cannot be moved to an Intel node, and vice versa.)
. Are there a sufficient number of CPU cores available on the destination?
. Is there sufficient RAM available on the destination?
. Is there sufficient access to required shared resources (VHD, network, and so on)?
. Is there sufficient access to physical device resources that must remain associated
with the virtual machine after migration (CD drives, DVDs, and LUNs or
offline disks)?
Migration cannot occur if there are any problems in the preflight stage. If there are, the virtual machine will remain on the source node and processing ends here. If preflight is successful, migration can occur and the virtual machine transfer continues.

4. The virtual machine state (inactive memory pages) moves to the target node to reduce the active virtual machine footprint as much as possible. All that remains on the source node is a small memory working set of the virtual machine. The virtual machine configuration and device information are transferred to the destination node and the worker process is created. Then, the virtual machine memory is transferred to the destination while the virtual machine is still running. The cluster service intercepts memory writes and tracks actions that occur during themigration. This page will be retransmitted later. Up to this point, the virtual
machine technically remains on the source node.

5. What remains of the virtual machine is briefly paused on the source node. The virtual
machine working set is then transferred to the destination host, storage access is
moved to the destination host, and the virtual machine is reset on the destination
host.

The only downtime on the virtual machine occurs in the last step, and this outage is
usually much less than most network applications are designed to tolerate. For example,
an administrator can be accessing the virtual machine via Remote Desktop while it is
being Live Migrated and will not experience an outage. Or a virtual machine could be
streaming video to multiple hosts, Live Migrated to another node, and the end users don’t know the difference.

Use the following steps to perform a Live Migration between two cluster nodes:
1. On one of the cluster nodes, open Failover Cluster Management.

2. Expand the Cluster and select Services and Applications.

3. Select the virtual machine to Live Migrate.

4. Click Live Migrate Virtual Machine to Another Node in the Actions pane and select the node to move the virtual machine to. The virtual machine will migrate to the selected node using the process described previously.

If there are processor differences between the source and destination node, Live Migration will display a warning that the CPU capabilities do not match. To perform a Live Migration, you must shut down the virtual machine and edit the settings of the processor to “Migrate to a Physical Computer with a Different Processor Version”.

Source of Information : Sams - Windows Server 2008 R2 Unleashed

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