VMware: VMotion CPU Compatibility Requirements for Intel Processors (1991)


Why am I unable to migrate virtual machines with VMotion across Intel processors?

In ESX 3.5 Update 2 and later, VMware recommends using Enhanced VMotion Compatibility (EVC) to eliminate many VMotion CPU compatibility problems. For more information on EVC, see KB 1003212.
To ensure system stability during migration with VMotion, VirtualCenter and vCenter Server require the source and target CPUs to be compatible. For more information on CPU compatibility requirements, see Basic System Administration for your version of VirtualCenter or vCenter Server, available from http://www.vmware.com/support/pubs/.

If the source and target CPUs are incompatible for VMotion, you can:

  • Perform a cold migration (rather than a VMotion migration), thereby removing VMotion CPU requirements as an issue.
  • Remove VMotion compatibility constraints by modifying the default bit-mask used by VirtualCenter or vCenter Server. Note that some modifications discussed in this knowledge base article are neither supported nor recommended by VMware for production environments. In general, masking any CPU features intended for applications (such as SSE3) is not supported for VMotion. Use of EVC is recommended for migrating virtual machines across CPU generations.

    To obtain more information about a host system’s CPU, you can use the CPU Identification Utility. VMware provides this as an ISO image file that can be uncompressed and used to create a bootable CD-ROM that provides CPU information about a host, even before an operating system or ESX is installed. The latest version of this tool can be found on the VMware downloads page at http://vmware.com/download/shared_utilities.html.
This knowledge base article discusses VMotion compatibility constraints for Intel CPUs. For detailed information about how to apply the masks discussed in this article, see knowledge base article 1993, “Migrations with VMotion Prevented Due to CPU Mismatch—How to Override Masks.” For information on AMD CPUs, see KB 1992.

VMotion Compatibility Groups for Intel Processors

To guarantee successful migrations with VMotion, VMware has defined several compatibility groups based on processor family (Pentium 4, Core) and features introduced within those families.

By default, VirtualCenter and vCenter Server support VMotion migrations within each CPU compatibility group. For example, migration within group A is allowed, but migration from group A to group B or from group B to group C is not, as shown in the tables.

Intel Pentium 4 CPUs

VMotion CPU Compatibility Group CPU Details


ESX Server 3.x and ESX 4.x


ESX Server 2.x

Group A
Without SSE3, without XD (eXecute Disable).

Models include:

  • Intel P4s prior to Model 3, Stepping 1.
    For example, Willamette and Northwood.
  • Xeon and Xeon MP CPUs prior to Nocona, Q3 2004. For example, Foster, Prestonia, and Gallatin.
For A <-> B VMotion, apply SSE3 mask (not supported).







For A <-> B VMotion, apply SSE3 mask (not supported).


Group B
(Group B and C are the same for VC 1.x)


With SSE3, without XD.
Models include:

P4s from Model 3, Stepping 1 to Model 4, Stepping 1.
For example, Prescott, or numbered 5×0, 5×5, 5×9.


For B <-> C VMotion, apply NX mask (supported).


Group C
(Group B and C are the same for VC 1.x)


With SSE3 and XD.
Models include:

P4s after Model 4, Stepping 1 onward and Xeon and Xeon MP with 64-bit (EM64T) enabled.
For example, Irwindale, Cranford, Dempsey, Tulsa, or numbered 50xx, 70xx, or 71xx.

Intel Core CPUs

VMotion CPU Compatibility Group
CPU Details
ESX 4.x, ESX Server 3.x, and ESX Server 2.x
Group A
Without SSSE3, SSE4.1, or SSE4.2.
Models include:
Dual-core Xeon LV based on Intel Core microarchitecture.
For example, Sossaman.
For A<->B VMotion, apply SSSE3 mask (not supported).
Group B
With SSSE3. Without SSE4.1 or SSE 4.2.
Models include:
Intel Xeon CPUs based on the Intel Core microarchitecture. For example, Intel Xeon 30xx, 32xx, 51xx, 53xx, 72xx, or 73xx.
For B<->C VMotion, apply SSE4.1 mask (not supported).
Group C
With SSSE 3 and SSE4.1. Without SSE4.2.
Models include:
Intel Xeon CPUs based on 45nm Intel Core microarchitecture. For example, Intel Xeon 31xx, 33xx, 52xx, 54xx, or 74xx.
For C<->D VMotion, apply SSE4.2 mask (not supported).
Group D
With SSSE3, SSE4.1, and SSE4.2.
Models include:
Intel Xeon CPUs based on Intel Nehalem microarchitecture (Core i7). For example, Intel Xeon 55xx.

Applying the Masks

For information about how to apply masks referenced in the tables, see KB 1993 under the section titled "Modifying the Default Mask".
Warning: For production environments, VMware neither supports nor recommends modifying CPU masks for SSE3, SSSE3, SSE4.1, or SSE4.2, because of the risk of failure in applications or the guest operating system after migration.

VMotion Between Single-Core and Multi-Core Processors

Migrations between single-core and multi-core Intel processors are supported, as long as the source and target CPUs have compatible CPU features (or the features are masked) as outlined in the tables above. 

For More Information

For more information about the Intel Pentium 4 CPU family, go to: http://www.intel.com/support/processors/pentium4/
For more information about Intel Xeon processors, go to: http://support.intel.com/support/processors/xeon/
For more information about SSE3, SSSE3, and SSE4, see the Intel 64 and IA-32 Architectures Software Developer’s Manual, Volume 1: Basic Architecture: http://www.intel.com/products/processor/manuals/
Note: Knowlege base articles 1991, 1992, and 1993 replace KB article 1377.

Source: 1991

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