Taking a Fresh Look at Hyper-V Clusters (Part 4)

If you would like to read the other parts in this article series please go to:

Introduction

In the previous article in this series, I showed you how you could build a failover cluster for the purpose of hosting Hyper-V virtual machines. In this article, I want to continue the discussion by showing you how to make your virtual machines fault tolerant. From there, I want to show you some of the options that are available for interacting with your fault tolerant virtual machines.

Making Your Virtual Machines Fault Tolerant

Before you can make a Hyper-V virtual machine highly available, you must understand the concept of a role. When it comes to failover clustering, a role can be thought of as a function that can be made highly available. For example, you can create a DHCP Server role or a File Server role through the Failover Cluster Manager. Although it might be tempting to think of Hyper-V virtual machines in some other way, the Failover Clustering Manager treats virtual machines as roles. This means that even though a Hyper-V server might participate as a node within a failover cluster, you aren’t actually making Hyper-V fault tolerant. Instead, you must make individual virtual machines fault tolerant by configuring those virtual machines as roles.

To make a virtual machine fault tolerant, open the Failover Cluster Manager (you can find it on the Server Manager’s Tools menu), and then select the Roles container and click on Configure Role link. This will cause Windows to launch the High Availability Wizard. Click Next to bypass the wizard’s Welcome screen and you will be taken to the role selection screen. Choose the Virtual Machine option, as shown in Figure A, and click Next.

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Figure A: Choose the Virtual Machine option and click Next.

At this point, you will see a list of all of the virtual machines that are running on any of the nodes within the cluster, as shown in Figure B. Keep in mind that these virtual machines can be on any cluster node. As you have probably guessed, you can select a virtual machine, click Next a few times, and the virtual machine will be made highly available.

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Figure B: This is a list of the virtual machines that can be made fault tolerant.

Before you actually click through and make a virtual machine fault tolerant, there is something else that you need to do. You must ensure that the virtual machine resides on cluster storage. Otherwise, when you make the virtual machine highly available, you will see a confirmation message indicating that “High Availability was Successfully Configured for the Role”. If you look at the dialog box shown in Figure C however, you will notice that there is a warning message that goes along with the confirmation. When you click the View Report button, you will see a message similar to the one shown in Figure D, stating that a disk is required by the virtual machine, but the disk has not been added to the cluster.

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Figure C: Windows generates a message indicating that the virtual machine was successfully made highly available.

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Figure D: The report indicates that a disk is required by the virtual machine, but has not been added to the cluster.

So why are we getting this warning? Well, there are a couple of different reasons. If you take a closer look at the error message shown above, you will notice that it states that “The following disk path was found to be required by the virtual machine ‘Lab1-Exch2013 Mailbox 3’, but is on a disk that has not yet been added to the cluster: ‘f:\vms’. This disk must be added to the cluster to make this virtual machine highly available.

The main reason why we are getting the warning message has to do with the fact that the virtual machine currently resides on local storage, rather than on cluster storage. In some situations it might be possible to add the virtual machine’s current storage location to the cluster as the dialog box shown above indicates. However, there are some requirements for doing so. For starters, the storage location has to be accessible to all the nodes in the cluster. Second, the disk must be defined as a basic disk. Dynamic disks are not supported. The system from which the above screen capture was taken is configured to use dynamic disks, so adding that particular disk to cluster storage isn’t an option. Under normal circumstances however, you could navigate through the console tree to Storage | Disks and then click on the Add Disk link to add storage to the cluster.

Virtual Machines Management

Once a virtual machine has been made fault tolerant, there are a number of different ways in which the virtual machine can be managed. You can manage the virtual machine through the Hyper-V Manager, the Failover Cluster Manager, or System Center Virtual Machine Manager. So which should you use?

When it comes to virtual machine management, it is important to understand the way that the various pieces of your virtualization solution fit together. Hyper-V is the hypervisor. It is what actually runs the virtual machines. The Failover Clustering feature might provide high availability for virtual machines, but regardless of how the virtual machines might be exposed through the Failover Cluster Manager, it is ultimately Hyper-V that runs the virtual machines. Similarly, System Center Virtual Machine Manager is a management tool. It exposes various Hyper-V and failover clustering capabilities, but it does not actually run the virtual machines or handle virtual machine failovers.

So with that said, let’s go back to the question of which management tool you should be using. In my opinion, if you have System Center Virtual Machine Manager then you should use that as your primary management tool. Otherwise, it is best to use the Failover Cluster Manager for the creation and management of any highly available virtual machines (non-fault tolerant virtual machines can be managed through the Hyper-V Manager).

In case you are wondering, the Failover Cluster Manager exposes most of the same management controls as the Hyper-V Manager. For example, as you can see in Figure E, you can use the Failover Cluster Manager to connect to a virtual machine, adjust virtual machine settings, replicate a virtual machine, and even live migrate virtual machines.

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Figure E: The Failover Cluster Manager exposes most of the same settings as the Hyper-V Manager.

So why not just use the Hyper-V Manager to do all that? Well, it comes down to efficiency. The Hyper-V Manager takes a server-centric view of your virtualization infrastructure. Imagine for a moment that you have ten Hyper-V servers. It is possible to configure the Hyper-V Manager to show all ten servers, but if you want to manage a specific virtual machine then you have to figure out which of the ten servers it resides on.

In contrast, the Failover Cluster Manager takes a role centric view of your virtual machines. The console lists all of the highly available virtual machines in the cluster, regardless of which server is hosting them. This is important because virtual machine locations are anything but static. A virtual machine can be moved to a different server at any time, so it’s nice to have a centralized view of the virtual machines. Admittedly, the console can become a bit crowded if you have a lot of virtual machines, but as you will notice in the previous screen capture, the console provides a Search field that you can use to locate a specific virtual machine.

Conclusion

Now that I have covered the basics of failover clustering, I want to move on and show you some other techniques. In the next article in the series, I will show you how to manage a cluster through System Center Virtual Machine Manager. From there, I am going to talk about virtual machine prioritization and optimization as it related to failover clustering.

If you would like to read the other parts in this article series please go to:

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