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Easy to say. But how do you configure this? Where do you find these options? You'll find out in this post.
Instead of disabling HA or DRS for the whole cluster, by using the VM Overrides option you can take a granular approach and disable HA and/or DRS settings at the VM level.
But you can't configure that option by selecting the VM and editing its settings. You must do it at the cluster level. This means that you select the cluster where the VM runs and apply the new settings there.
Many VMware users have perfect knowledge of the free version of ESXi. But this version does not allow you to configure DRS, HA, or vMotion. You must have two or more hosts, and those hosts must be connected to the shared storage where the VMs are stored.
When you create a vSphere DRS cluster, you can override the default automation behavior of the cluster on a per-VM basis. This means that you can exclude an individual VM from the cluster-wide settings.
You can find VM Overrides at the Cluster level under the Configure menu. In the image below, you can see that you select vCluster. Go to Configure, and under Configuration click on VM Overrides.
The DRS cluster can have the automation level configured as Fully Automated. In this case, all VMs are moved around to accommodate the host's load, and no single host is overloaded.
You can configure the VM Override to Manual; in which case, the VM is excluded from the cluster-wide configuration.
This is pretty handy in many scenarios where you do not want a particular VM to be moved around by DRS; for example, a vCenter Server VM (or VCSA).
There are four options in all:
- Disabled – You will disable DRS automation completely for this VM.
- Manual – You will receive notifications from your DRS for manual vMotion tasks.
- Partially Automated – This option provides an initial placement automatically. However, migration recommendations are only displayed; they do not run.
- Fully Automated – This option provides default settings on a per-cluster basis.
On the same screen, you can set options for what happens with this VM when there is an HA failover. A VM can have various restart priorities. You can choose from the following options: Lowest, Low, Medium, High, Highest, and Disabled.
In our case of a VMware vCenter server VM, you would want to use the Highest option, since this VM must be restarted before anything else--perhaps even before a domain controller VM, since the initialization of the internal DB takes at least five minutes.
Each virtual machine in a vSphere HA cluster is assigned the cluster default settings for VM Restart Priority.
You can change the default behavior for each virtual machine by changing these defaults. However, If the virtual machine leaves the cluster, these settings are lost, because they are settings at the cluster-level.
During migration of VMs from one datacenter to another, you should always check these rules and exceptions. Otherwise, they're simply lost. They do not migrate along with a particular VM(s).
Note: If you plan to use vSphere fault tolerance, you should keep in mind that DRS will not move fault tolerance–enabled virtual machines.
Microsoft Cluster Service (MSCS) virtual machines ^
If you have any Microsoft Clustered VMs, the automation level of all virtual machines in an MSCS cluster should be set to Partially Automated. This is VMware's recommendation.
When you set the vSphere DRS automation level for the virtual machine to Partially Automated, vCenter Server will perform an initial placement of VMs when they are powered on and will provide migration recommendations for them. (Not actual vMotion.)
So let's say you have three VMs with a Microsoft MSCS configuration. In this case, you should select all three VMs and apply this configuration so that they will not be affected by DRS and vMotion but will still be protected by VMware High Availability (HA) and will be restarted if the underlying hardware has any problems.
Final words ^
This behavior has been changed several times in VMware vSphere. The above screenshots are from the latest release of VMware vSphere, 6.7 Update 2.
The VM Overrides option is useful when you have a VM or VMs that you do not want to be affected by your cluster-wide settings. As you see, you have several options at your fingertips and can choose a configuration that suits your needs.
You can also use VM-VM or Host-VM affinity and anti-affinity rules whenever you need them. An enterprise environment can have very specific use cases, and VMware vSphere cluster options as well as various override options enable you to provide an accurate configuration for your virtual environment.
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All settings can be managed from a single console by using the vSphere HTML 5 client. Only rarely do you need to use a specific configuration at the VM level (via a VM hardware option).