Enhanced vMotion Compatibility (EVC)

Enhanced vMotion Compatibility which is a vCenter Server cluster-centric feature allowing virtual machines to vMotion or migrate across ESXi hosts equipped with dissimilar processors in the same cluster. VMware EVC Mode works by masking unsupported processor features thus presenting a homogeneous processor front to all the virtual machines in a cluster. This means that a VM can vMotion to any ESXi host in a cluster irrespective of the host’s micro-architecture examples of which include Intel’s Sandy Bridge and Haswell. One thing to remember is that all the processor(s) must be from a single vendor i.e. either Intel or AMD. You simply cannot mix and match.

Benefit

The main benefit is that you can add servers with the latest processors to your existing cluster(s) seamlessly and without incurring any downtime. More importantly, EVC provides you with the flexibility required to scale your infrastructure, lessening the need to decommission older servers prematurely, thus maximizing ROI. It also paves the way for seamless cluster upgrades once the decision to retire old hardware is taken.

Any Impacts

When a new family of processors is released to market, innovative microprocessor features and instruction sets are often included. These features include performance enhancements in areas such as multimedia, graphics or encryption. With this in mind try to determine in advance the type of applications you’ll be running in your vSphere environment. This gives you a rough idea of the type of processors you’ll be needing. This, in turn, allows you to predetermine the applicable EVC modes when mixing servers with processors from different generations. EVC modes are also dependent on the version of vCenter Server. This is shown in Figure 1 below (Intel based EVC modes)

Requirement

To enable EVC, you must make sure the ESXi hosts in your cluster satisfy the following.

• Processors must be from the vendor, AMD or Intel.
• Hosts must be properly configured for vMotion.
• Hosts must be connected to the same vCenter Server.
• Advanced virtualization features such as Intel-VT and AMD-V must be enabled for all hosts from the server’s BIOS.

Use the VMware Compatibility Guide to assess your EVC options

The VMware Compatibility Guide is the best way to determine which EVC modes are compatible with the processors used in your cluster. Please check below example on how to determine which EVC mode to use given 3 types of Intel processors.

The steps are as follows;

• Select the ESXi version installed.

• Hold down the CTRL key and select the type of processors from the CPU Series list.

• Press the CPU/EVC matrix button to view the results.

The results tell us that we can only use EVC modes Merom or the Penryn. This means we have to sacrifice some features exclusive to the Intel i7 processor. This is the stage at which you have to decide whether you’re better off getting new servers as opposed to adding old servers to the cluster.

Check  How to enable EVC