Strong Together

Dynamic I/O

Clusters on Windows Server 2012 R2 support dynamic I/O. If the data connection of a node fails, the cluster can automatically route the traffic that is necessary for communication to the virtual machines on the SAN through the lines of the second node, without having to perform a failover. You can configure a cluster so that the cluster node prioritizes network traffic between the nodes and to CSVs.

Managing Virtual Servers in the Cluster

To create a virtual server in a cluster, use the Failover Cluster Manager. Right-click Roles | Virtual Machines  | New Virtual Machine to launch the wizard. Select the cluster node on which you want to deploy this server. The rest of the wizard is similar to the virtual server configuration. Where created, the virtual servers appear in the Roles section of the Failover Cluster Manager. Use the context menu to manage the virtual server.

To start a live migration, right-click the virtual machine (Figure 7), select the Move | Live Migration context menu entry, and then select the node. First, however, you need to configure live migration in the Hyper-V settings on the appropriate Hyper-V hosts. The difference between live migration and quick migration is that machines remain active while crossing the wire for a live migration and the memory content is transferred between the servers. In fast migration, Hyper-V disables the machines before migrating.

Figure 7: Virtual machines are managed in the Failover Cluster Manager.

You can configure a 2012 R2 cluster with Windows Server so that the cluster nodes prioritize network traffic between the nodes and the shared volumes. To learn which network settings the cluster uses to communicate with the cluster shared volume, start a PowerShell session on the server and run the commandlet Get-ClusterNetwork.

Another new feature in Windows Server 2012 is the Change Startup Priority section in the context menu of virtual servers. Here, you can specify when virtual servers are allowed to start. Another new feature is the ability to set up monitoring for virtual servers in the cluster. You can find this setting in More Actions  | Configure Monitoring . Then, select the services to be monitored by the cluster. If one of the selected services fails on the virtual machine, the cluster can restart the VM or migrate it to another node.

VHDX Shared Disks

Besides being able to use physical disks and iSCSI targets for the cluster, you can use the new sharing function for VHDX disks in Windows Server 2012 R2. To do so, you create one or more virtual disks that you then assign to one of the virtual cluster nodes via a virtual SCSI controller.

Go to the settings for the virtual server and select SCSI Controller  | Hard Drive | Advanced Features . Click the checkbox for Enable virtual hard disk sharing (Figure 8). Now you have the ability to assign this virtual disk to different virtual servers and, thus, use it as shared storage. On the basis of this virtual disk, you then build a cluster with virtual servers in Hyper-V or some other virtualization solution. This makes it very easy to build virtual clusters.

Figure 8: You can share virtual disks in Windows Server 2012 R2 and use them in the cluster.

To be able to use the shared VHDX function, the virtual servers need to be located in a cluster. Additionally, the virtual disks provided by shared VHDX must be stored on a shared disk in the cluster. It is best to use the configured CSV for this. That means that you cannot use shared VHDX disks in Windows 8.1, even if this function is theoretically available. For test purposes, you can also easily create a cluster with only one node. Although this scenario is not officially supported, it does work.

You cannot modify shared storage on the fly, for example, to change the size of disks. This process is only allowed for normal virtual disks, which are assigned to virtual SCSI controllers. This feature is new in Windows Server 2012 R2. Also, it is impossible to perform live migration of the memory for virtual hard disks that you use as shared VHDX in the cluster. Again, that is only possible with normal hard disks, even on Windows Server 2012.