Hot and Cold Migrations; Which Network is Used?

–originally authored and posted by me at https://blogs.vmware.com/vsphere/2020/03/how-is-virtual-memory-translated-to-physical-memory.html–

A common question arises when customers are migrating workloads between ESXi hosts, clusters, vCenter Servers or data centers. What network is being used when a hot or cold migration is initiated? This blog post explains the difference between the various services and networks stacks in ESXi, and which one is used for a specific type of migration.

How do we define what is a hot or cold migration? A cold workload migration is a virtual machine that is powered off in the entire duration of migration. A hot migration means that the workload and application will remain available during the migration.

Both hot and cold migrations can be initiated through the vCenter Server UI or in an automation fashion using, for example, PowerCLI. To understand which network is used for a migration, we first need to understand the various enabled services and network stack options that are available in vSphere.

Enabled Services

In vSphere, we define the following services that can be enabled on VMkernel interfaces:

  • vMotion
  • Provisioning
  • Fault Tolerance logging
  • Management
  • vSphere Replication
  • vSphere Replication NFC (Network File Copy)
  • vSAN

When looking specifically into workload migrations, three services play an important role. The vMotion, Provisioning and Management enabled networks.

Enabling a service on a specific VMkernel interface, states that this network can now be used for the configured service. While the Management service is enabled by default on the first VMkernel interface, the other VMkernel interfaces and services are typically configured post-installation of ESXi. If you want vMotion or Provisioning traffic to use a specific VMkernel interface, you can configure it like that. (more…)

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