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Placing Virtual Machines on Hosts

Updated: August 14, 2009

Applies To: Virtual Machine Manager 2008, Virtual Machine Manager 2008 R2, Virtual Machine Manager 2008 R2 SP1

When you deploy or migrate a virtual machine to a host, the evaluation and selection of the most suitable host for the virtual machine is known as virtual machine placement, or placement. During placement, Virtual Machine Manager (VMM) evaluates the suitability of available hosts and assigns each host a rating of 0 stars (not suitable) through 5 stars (very suitable), in half-star increments. Each host’s rating is based on several factors, including the virtualization software on the host, the hardware and networking configuration of the host and the virtual machine, the virtual machine's resource requirements, and whether the virtual machine is highly available.

A new feature in VMM 2008 R2 is the host compatibility check, which VMM performs before migrating a virtual machine that is deployed on a Hyper-V host cluster created in Windows Server 2008 R2. To prevent a migration from failing, the host compatibility check ensures that the destination host’s hardware, such as CPU model, is compatible with the source host. VMM uses the Hyper-V compatibility check API in Windows Server 2008 R2 and the VMware compatibility check APIs to ensure that hardware requirements are met for each type of virtualization software. This feature is not available for failover clusters created in Windows Server 2008.

ImportantImportant
In VMM 2008 R2, for hosts that are running Windows Server 2008 R2 or for ESX Server hosts, the ratings that first appear on the Select Host wizard page are based on a preliminary evaluation by VMM. To see a host rating based on a more thorough evaluation, you must select the host by clicking it.

Automatic Placement

VMM automatically places a virtual machine on the most suitable host in a host group and the most suitable volume on a host based on the volume's available space. This process is known as automatic placement, and it occurs in the following situations:

  • When you drag a virtual machine onto a host or a host group in Virtual Machines view.

  • When self-service users deploy virtual machines that they create by using the VMM Self-Service Portal. For more information about self-service, see About Virtual Machine Self-Service.

    ImportantImportant
    A default virtual machine path must be configured on the volume that VMM selects during automatic placement or the virtual machine placement will fail. For more information about how to add default virtual machine paths on hosts, see How to Set Placement Options for a Host.

During automatic placement, the files for the virtual machine are moved to the most suitable host for a host group, and to the most suitable volume on the selected host based on the volume's available space. For automatic placement to succeed, you must configure a default virtual machine path on the recommended volume. For more information, see About Default Virtual Machine Paths (http://go.microsoft.com/fwlink/?LinkID=162784).

noteNote
If you configured a virtual machine with the hardware configuration Make this VM highly available, only clustered Hyper-V hosts and ESX Server hosts in a host cluster are rated as highly available by VMM. For more information, see How to Configure Virtual Machine Priority and Availability.

Customizing Host Ratings

The metrics for rating hosts can be customized for VMM. For information, see How to Set Placement Defaults for Virtual Machines. Host ratings also can be customized for individual virtual machines during deployment or migration. For more information, see How to Customize Host Ratings for a Virtual Machine.

Removing a Host from Placement

You might want to use some hosts only for performing maintenance tasks such as creating and patching virtual machines. To ensure that these hosts are not rated when you deploy or migrate a virtual machine, you can remove the hosts from placement. For more information, see How to Set Placement Defaults for Virtual Machines.

See Also

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