Understanding EVC Mode (vSphere) and when to use it

  • 4 March 2020
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Let’s say you want to add a new node with a newer processor class than the existing nodes in the cluster. In this case you must enable EVC (Enhanced vMotion Compatibility) feature.

 

What is EVC?

 

EVC stands for 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 caveat 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.

 

What are the benefits?

 

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.

 

Are there any disadvantages?

 

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.

Figure 1 - Intel based EVC modes (reproduced from VMware’s KB1003212)

Figure 1 – Intel based EVC modes (reproduced from VMware’s KB1003212)

  To apply this feature on a Nutanix Cluster you must shut down the cluster first, please follow this article: Shutting down Nutanix cluster running VMware vSphere for maintenance or relocation for detailed instructions. Then you can apply the EVC mode from a VSphere client following this step by step instructions: Verifying and Setting the CPU Type (VSphere).

 

To know more about the EVC feature read the following VMWare Blog : Enhanced vMotion Compatibility (EVC) Explained

  

Note: Consider a maintenance window in your production environment to apply this feature.


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