Cold migration is the migration of powered off or suspended virtual machines between hosts across clusters, data centers, and vCenter Server instances. By using cold migration, you can also move associated disks from one datastore to another.

You can use cold migration to have the target host checked against fewer requirements than when you use vMotion. For example, if you use cold migration when a virtual machine contains a complex application setup, the compatibility checks during vMotion might prevent the virtual machine from moving to another host.

You must power off or suspend the virtual machines before you begin the cold migration process. Migrating a suspended virtual machine is considered a cold migration because although the virtual machine is powered on, it is not running.

You cannot implement a cold migration across different subnets.

CPU Compatibility Check During Cold Migration

If you attempt to migrate a powered off virtual machine that is configured with a 64-bit operating system to a host that does not support 64-bit operating systems, vCenter Server generates a warning. Otherwise, CPU compatibility checks do not apply when you migrate powered off virtual machines with cold migration.

When you migrate a suspended virtual machine, the new host for the virtual machine must meet CPU compatibility requirements. This requirement allows the virtual machine to resume execution on the new host.

Operations During Cold Migration

A cold migration consists of the following operations:

  1. If you select the option to move to a different datastore, the configuration files, including the NVRAM file (BIOS settings), log files, and the suspend file, are moved from the source host to the destination host’s associated storage area. You can choose to move the virtual machine's disks as well.
  2. The virtual machine is registered with the new host.
  3. After the migration is completed, the old version of the virtual machine is deleted from the source host and datastore if you selected the option to move to a different datastore.

Network Traffic for Cold Migration

By default, data for VM cold migration, cloning, and snapshots is transferred through the management network. This traffic is called provisioning traffic. It is not encrypted but uses run-length encoding of data.

On a host, you can dedicate a separate VMkernel network adapter to the provisioning traffic, for example, to isolate this traffic on another VLAN. On a host, you can assign no more than one VMkernel adapter for provisioning traffic. For information about enabling provisioning traffic on a separate VMkernel adapter, see the vSphere Networking documentation.

If you plan to transfer high volumes of virtual machine data that the management network cannot accommodate, redirect the cold migration traffic on a host to the TCP/IP stack that is dedicated to cold migration and cloning of powered off virtual machines. You can also redirect if you want to isolate cold migration traffic in a subnet different from the management network, for example, for migration over a long distance. See How to Place Traffic for Cold Migration, Cloning, and Snapshots on the Provisioning TCP/IP Stack.

How to Migrate a Powered Off or Suspended Virtual Machine

You can use cold migration to move a virtual machine and its associated disks from one datastore to another in your vSphere environment. The virtual machines are not required to be on shared storage.

Prerequisites

Procedure

  1. Power off or suspend the virtual machine.
  2. Right-click the virtual machine and select Migrate.
    1. To locate a virtual machine, select a data center, folder, cluster, resource pool, host, or vApp.
    2. Click the Virtual Machines tab.
  3. Select the migration type and click Next.
    Option Description
    Change compute resource only Move the virtual machine to another host.
    Change storage only Move the virtual machine’s configuration file and virtual disks.
    Change both compute resource and storage Move the virtual machine to another host and move its configuration file and virtual disks.
  4. If you change the compute resource of the virtual machine, select the destination compute resource for this virtual machine migration and click Next.

    Any compatibility problem appears in the Compatibility panel. Fix the problem, or select another host or cluster.

    Possible targets include hosts and DRS clusters with any level of automation. If a cluster has no DRS enabled, select a specific host in the cluster rather than selecting the cluster.

    Important:

    If the virtual machine that you migrate has an NVDIMM device and uses PMem storage, the destination host or cluster must have available PMem resources. Otherwise, the compatibility check fails and you cannot proceed further with the migration.

    If the virtual machine that you migrate does not have an NVDIMM device but it uses PMem storage, you must select a host or cluster with available PMem resources, so that all PMem hard disks remain stored on a PMem datastore. Otherwise, all the hard disks use the storage policy and datastore selected for the configuration files of the virtual machine.

    Important:

    Migrating a virtual machine that has an NVDIMM device or a vPMem disk to a host that does not have the proper license fails and leaves the virtual machine in an unmanageable state for 90 seconds. You can afterwards retry the migration and select a destination host that is licensed to use PMem devices.

  5. If you change the storage of the virtual machine, enter the required details in the Select Storage page.
    1. Select the storage type for the virtual machine configuration files and all the hard disks.

      • If you select the Standard mode, all virtual disks are stored on a standard datastore.

      • If you select the PMem mode, all virtual disks are stored on the host-local PMem datastore. Configuration files cannot be stored on a PMem datastore and you must additionally select a regular datastore for the configuration files of the virtual machine.

      • If you select the Hybrid mode, all PMem virtual disks remain stored on a PMem datastore. Non-PMem disks are affected by your choice of a VM storage policy and datastore or datastore cluster.

      Selecting the type of storage is possible only if PMem or Hybrid storage types are available in the data center.

    2. Select the format for the virtual machine disks.
      Option Action
      Same format as source Use the same format as the source virtual machine.
      Thick Provision Lazy Zeroed Create a virtual disk in a default thick format. Space required for the virtual disk is allocated during creation. Any data remaining on the physical device is not erased during creation. Instead, it is zeroed out on demand on first write from the virtual machine.
      Thick Provision Eager Zeroed Create a thick disk that supports clustering features such as Fault Tolerance. Space required for the virtual disk is allocated at creation time. In contrast to the thick provision lazy zeroed format, the data remaining on the physical device is zeroed out during creation. It might take longer to create disks in this format than to create other types of disks.
      Thin Provision Use the thin provisioned format. At first, a thin provisioned disk uses only as much datastore space as the disk initially needs. If the thin disk needs more space later, it can expand to the maximum capacity allocated to it.
    3. Select a virtual machine storage policy from the VM Storage Policy drop-down menu.

      Storage policies specify storage requirements for applications that run on the virtual machine. You can also select the default policy for vSAN or Virtual Volumes datastores.

      Important:

      If the virtual machine hard disks use different storage policies, the new policy that you select only applies to non-PMem hard disks. PMem hard disks are migrated to the host-local PMem datastore of the destination host.

    4. Select the datastore location where you want to store the virtual machine files.

      Option

      Action

      Store all virtual machine files in the same location on a datastore.

      Select a datastore from the list and click Next.

      Store all virtual machine files in the same Storage DRS cluster.

      1. Select a Storage DRS cluster.

      2. (Optional)

        To deactivate Storage DRS with this virtual machine, select Disable Storage DRS for this virtual machine and select a datastore within the Storage DRS cluster.

      3. Click Next.

      Store virtual machine configuration files and disks in separate locations.

      1. Click Configure per disk.

        Note:

        You can use the Configure per disk option to downgrade from or upgrade to PMem storage.

      2. For the virtual machine configuration file and for each virtual disk, select Browse, and select a datastore or Storage DRS cluster.

        Note:

        Configuration files cannot be stored on a PMem datastore.

      3. (Optional)

        If you selected a Storage DRS cluster and do not want to use Storage DRS with this virtual machine, select Disable Storage DRS for this virtual machine and select a datastore within the Storage DRS cluster.

      4. Click Next.
  6. If you change the compute resource of the virtual machine, select destination networks for the virtual machine migration.

    You can migrate a virtual machine network to another distributed switch in the same or to another data center or vCenter Server.

    Option

    Action

    Select a destination network for all VM network adapters connected to a valid source network.

    1. Click the arrow in the Destination Network column and select Browse.

    2. Select a destination network and click OK.

    3. Click Next.

    Select a new destination network for each VM network adapter connected to a valid source network.

    1. Click Advanced.

    2. Click the arrow in the Destination Network column and select Browse.

    3. Select a destination network and click OK.

    4. Click Next.
  7. On the Ready to complete page, review the details and click Finish.

Results

vCenter Server moves the virtual machine to the new host or storage location.

Event messages appear in the Events tab. The data displayed on the Summary tab shows the status and state throughout the migration. If errors occur during migration, the virtual machines revert to their original states and locations.