Misconception about vMotion Traffic usage:

Set of Common  questions always arise during  vSphere migration design discussions , like what network / interface used for migration  ? How to perform the network segmentation for optimal migration experience without any impacts. What exactly gets transferred in VMotion enabled networks .

There are multiple different opinions about the data flow in migration networking and most of the percentage misunderstand that the vMotion networking is solely responsible for VM migration in all scenarios,  even during storage vMotion and thus resulting in improper planning and can cause potential  performance issues during the actual migration.

Lets dig in deeper to understand based on scenarios:

There are two states in VM migration:

  1. Cold Migration ( virtual machine that is powered off in the entire duration of migration – Cold data)
  2. Hot Migration  (virtual machine is powered on and actively available during the migration – Hot Data)

Table below depicts the vMotion networking usage with scenarios.

Item NoMigration ActionMigration StateNetworking UsedNotes
1vMotion(Compute)HotvMotionTransfer only the ownership of the VM files like .vmx , .swp (we are not moving any data here, just change the VM ownership from host1 to host 2). Snapshots, Clones & vmdk will use management enabled network.
2vMotion(Compute)ColdManagementvMotion network is not used to perform this migration. cold data like powered off virtual machines, clones and snapshots are migrated over the Provisioning network if that is enabled. It is not enabled by default. If it’s not configured, the Management enabled network will be used.
3Storage vMotion(Storage)HotManagementvMotion network is not used to perform this migration.
All data (VMDKs) goes through Provisioning or Management enabled network.
4Storage vMotion(Storage)ColdManagementvMotion network is not used to perform this migration. All data (VMDKs) goes through Provisioning or Management enabled network
5xMotion(Compute + Storage)HotvMotion + ManagementHot data like .vmx. .swp will go through vMotion enabled network (like Item No1) and rest go through Provisioning or Management enabled network
6xMotion(Compute + Storage)ColdManagementvMotion network is not used to perform this migration. All data (VMDKs) goes through Provisioning or Management enabled network

Additional Points to be considered:

  • Management service is enabled by default on the first VMkernel interface, the other VMkernel interfaces and services are typically configured post-installation of ESXi. This can be customized based on our design requirements
  • You can test yourself the traffic flow with the help of wireshark inspection and also, like disabling the vmotion when migrating the cold VM and observe.

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