HPE SimpliVity is a hyperconverged infrastructure solution that combines compute, storage, networking, and data services in a single appliance1. HPE SimpliVity clusters are groups of HPE SimpliVity nodes that share the same federation and data center2. HPE SimpliVity clusters can be expanded by adding new nodes to increase the capacity and performance of the cluster3.
However, adding new nodes with newer generation Intel CPUs to an existing HPE SimpliVity cluster may cause compatibility issues for vMotion, the VMware technology that enables live migration of virtual machines between hosts4. vMotion requires that the source and destination hosts have compatible CPUs, meaning that they support thesame set of CPU features4. If the new nodes have different or additional CPU features than the existing nodes, vMotion may fail or be restricted4.
To facilitate adding the new hosts to the cluster, one possible solution is to enable Enhanced vMotion Compatibility (EVC) on the cluster5. EVC is a feature of VMware vSphere that ensures vMotion compatibility for the hosts in a cluster that are running different CPU generations5. EVC masks the CPU features that are not common among all hosts in the cluster, so that all hosts present the same CPU feature set to the virtual machines5. This way, vMotion can be performed without CPU compatibility errors5.
To enable EVC on the cluster, the following steps are required5:
Power off all virtual machines in the cluster, or migrate them to another cluster.
Edit the cluster settings and select the EVC mode that corresponds to the baseline CPU feature set for the cluster. The EVC mode must be equivalent to or a subset of the feature set of the host with the smallest feature set in the cluster.
Add the new hosts to the cluster and verify that they are compatible with the EVC mode.
Power on the virtual machines in the cluster, or migrate them back from another cluster.
By enabling EVC, the cluster can benefit from the improved vMotion compatibility and flexibility of adding new hosts with newer generation Intel CPUs. However, enabling EVC also has some limitations and trade-offs, such as5:
EVC does not allow vMotion between hosts with different CPU vendors, such as AMD and Intel.
EVC does not prevent vMotion from failing for other reasons, such as network or storage incompatibility.
EVC may prevent virtual machines from accessing some CPU features that are available on newer hosts, but not on older hosts.
EVC may not work with some applications that do not follow the CPU vendor recommended methods of feature detection.
Therefore, enabling EVC should be carefully planned and tested before adding the new hosts to the cluster.
References:
1: HPE SimpliVity
2: HPE SimpliVity User Guide
3: HPE SimpliVity Expansion Installation and Startup Service
4: VMware EVC and CPU Compatibility FAQ
5: About Enhanced vMotion Compatibility
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