Enhanced vMotion Capability (EVC) in VMWare vSphere 5

Enhanced vMotion Capability (EVC) in VMWare vSphere 5

VMware Enhanced vMotion Compatibility (EVC) facilitates vMotion between different CPU generations through use of Intel Flex Migration and AMD-V Extended Migration technologies. When enabled, EVC ensures that all CPUs within the cluster are vMotion compatible.

What is The Benefit Of EVC?

Because EVC allows you to migrate virtual machines between different generations of CPUs, older and newer server generations can be mixed in the same cluster and still allow vMotion migration between these hosts. This makes adding new hardware into your existing infrastructure easier and helps extend the value of your existing hosts.

How Does EVC Work?

EVC leverages a defined baseline that allows all the hosts in the cluster to advertise the same CPU feature set. The EVC baseline does not disable the features within a CPU, but indicates to a virtual machine that specific features are not available.It is crucial to understand that EVC only focuses on CPU features specific to CPU generations, such as SIMD (SSE) or AMD-now instructions. EVC hides these CPU features from software running inside virtual machines by not advertising these features. This means that the features

are still available and active, but they are not “publically broadcasted.” When enabling EVC, a CPU baseline must be selected. This baseline represents a feature set of the selected CPU generation and exposes specific CPU generation features. When a virtual machine powers-on within an EVC cluster, this cluster’s baseline will be attached to the virtual machine until it powers-off.

Note

The EVC baseline is attached to the virtual machine until it powers off even if it is migrated to another EVC cluster.

If an ESXi host with a newer generation CPU is joined to the cluster, the baseline will automatically “hide” the CPU features that are new and unique to that CPU generation.

Enabling And Disabling EVC

EVC can be enabled even when virtual machines are active. Powered-on virtual machines will not block configuration of EVC for a cluster as long as the virtual machine itself is compatible with the desired EVC mode.

If EVC is disabled, the virtual machines continue to operate at the same EVC mode and are not forced to restart. If complete removal of the EVC mode is required, the virtual machine must go through a complete power-cycle; a reboot is not sufficient.

It is important to remember that EVC baselines are applied only during power-on operations. If the EVC cluster mode is changed, active virtual machines are required to complete a full powercycle to receive the new baseline.

EVC Requirements

To enable EVC on a cluster, the cluster must meet the following requirements:

-  All hosts in the cluster must have CPUs from a single vendor, either AMD or Intel.

-  All hosts in the cluster must have advanced CPU features, such as hardware virtualization support (AMD-

   V or Intel VT) and AMD No eXecute (NX) or Intel eXecute Disable (XD) and must be enabled in the 

    BIOS.

-  All hosts in the cluster should be configured for vMotion. See the section, Host Configuration 

    Requirements for vMotion.

-  All hosts in the cluster must be connected to the same vCenter Server system. In addition, all hosts in the 

    cluster must have CPUs that support the EVC mode you want to enable. 

To check EVC support for a specific processor or server model, see the VMware Compatibility Guide.