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VM migration lifecycle

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This page describes the phases a particular VM undergoes during a migration to Google Cloud. Some phases are optional, and others are unavailable during cloud-to-cloud migrations.

Full migration

The full migration operation moves VMs in one step from source to target. In doing so, it:

  1. Performs the run-in-cloud process.
  2. Waits for the VMs to be in the Cache on Demand state, when storage is streamed to the cloud.
  3. Migrates the VM data to Google Cloud.
  4. After storage is fully copied to Google Cloud, prepares the VM to detach.

When this process has completed, the VM state changes to Ready to Detach.

Full migration is an automatic process that includes the following tasks (which you can also run manually).


This operation moves the source VMs from your on-premises data center to Google Cloud. This does not completely move VM storage to the cloud -- you migrate storage with storage migration.

The run-in-cloud operation:

  1. Shuts down the source VMs.
  2. Attaches to the VM's volumes.
  3. Starts the VM on Google Cloud, streaming storage as needed.

Storage migration

This operation copies storage data associated with a migrating VM to a disk on Compute Engine. To learn more about storage migration, see Migrating on-premises storage.

Prepare to detach

This operation takes VM disks from the Migrate for Compute Engine cache and object store and creates the native data drives in Google Cloud. After this operation finishes, you can detach the VM from the Migrate for Compute Engine cache.


In the detach sequence, Migrate for Compute Engine:

  • Shuts down the VM in the cloud.
  • Performs any final data synchronization necessary.
  • Attaches the native disks to the instance.
  • Starts the instance in Google Cloud.

Upgrade OS

This operation upgrades the OS of qualified VMs in the wave. For more on upgrading OSes during migration, see Upgrading Windows Server VMs.

If you perform the Upgrade OS operation, you must run it after you successfully run the Detach operation and before you run the Cleanup operation.

During the upgrade sequence, Migrate for Compute Engine:

  • Shuts down the VM on Compute Engine.
  • Upgrades the VM OS.


After the VMs are detached and you have completed any required validation, you can start the detach cleanup. Each VM is then marked as unmanaged by Migrate for Compute Engine.

You can Move back at any time before you run Cleanup.

Move back

Moves the instances in Google Cloud back to their source, either on-premises or AWS.

The move-back operation:

  1. Stops the VMs.
  2. Moves storage back to source.
  3. Deletes the Google Cloud instances.

Test clone

A test clone creates clones of selected VMs to test them in Compute Engine. The test clone behaves like the live systems and leverages data from the source VM. However, test clones do not modify any live data because data from the test environment is not written back on-premises. Upon creating a test clone, Migrate for Compute Engine:

  1. Attaches to the VM volumes.
  2. Starts each instance in Google Cloud. Storage is streamed from the VM to Google Cloud.

For more information about how to use test clones, see Testing migrated workloads.

Delete clone

Deleting the test clone removes it from Google Cloud.

Note that deleting the test clone has no impact whatsoever on your live system or data. Any changes made to data in the test clone are not replicated back to your live system.

Offline migration

Migrate for Compute Engine can migrate workloads with operating systems or file systems that Migrate for Compute Engine's streaming technology does not support, but that the cloud environment does support.

See Supported operating systems for a list of operating systems supported for offline migration.

During the offline migration process, Migrate for Compute Engine:

  1. Migrates storage.
  2. Starts the new VM only after migration is completed.
  3. Detaches the VM.