Scenarios: Using processor compatibility modes in partition mobility

Scenario: Migrating an active logical partition from a POWER7 processor-based server to a POWER8 processor-based server

You want to migrate an active logical partition from a POWER7® processor-based server to a POWER8® processor-based server so that the logical partition can use the additional capabilities available with the POWER8 processor-based server.

To migrate an active logical partition from a POWER7 processor-based server to a POWER8 processor-based server, complete the following steps:

1. Set the preferred processor compatibility mode to the default mode. When you activate the logical partition on the POWER7 processor-based server, it runs in the POWER7 mode.
2. Migrate the logical partition to the POWER8 processor-based server. Both the current and preferred modes remain unchanged for the logical partition until you restart the logical partition.
3. Restart the logical partition on the POWER8 processor-based server. The hypervisor evaluates the configuration. Because the preferred mode is set to default and the logical partition now runs on a POWER8 processor-based server, the highest mode available is the POWER8 mode. The hypervisor determines that the most fully featured mode supported by the operating environment installed in the logical partition is the POWER8 mode and changes the current mode of the logical partition to the POWER8 mode.

At this point, the current processor compatibility mode of the logical partition is the POWER8 mode and the logical partition runs on the POWER8 processor-based server.

Scenario: Migrating the active logical partition back to the POWER7 processor-based server

A problem arises and you need to migrate the active logical partition back to the POWER7 processor-based server. Because the logical partition now runs in the POWER8 mode and the POWER8 mode is not supported on the POWER7 processor-based server, you need to adjust the preferred mode for the logical partition so that the hypervisor can reset the current mode to a mode that is supported by the POWER7 processor-based server.

To migrate the logical partition back to the POWER7 processor-based server, complete the following steps:

1. Change the preferred mode from the default mode to the POWER7 mode.
2. Restart the logical partition on the POWER8 processor-based server. The hypervisor evaluates the configuration. Because the preferred mode is set to POWER7, the hypervisor does not set the current mode to a higher mode than POWER7. The hypervisor first determines whether it can set the current mode to the preferred mode. If not, it determines whether it can set the current mode to the next highest mode, and so on. In this case, the operating environment supports the POWER7 mode, so the hypervisor sets the current mode to the POWER7 mode.
3. Now that the logical partition runs in the POWER7 mode and the POWER7 mode is supported on the POWER7 processor-based server, migrate the logical partition back to the POWER7 processor-based server.

Scenario: Migrating an active logical partition between different processor types without changing the configuration settings

Depending on how often you want to migrate logical partitions, you might want to maintain the flexibility to migrate an active logical partition between a POWER7 processor-based server and a POWER8 processor-based server so that you can migrate the logical partition back and forth without changing the configuration settings. To maintain this type of flexibility, determine the processor compatibility mode supported on both the source and destination servers and set the preferred processor compatibility mode of the logical partition to the highest mode supported by both servers.

To accomplish this flexibility, complete the following steps:

1. Set the preferred processor compatibility mode to the POWER7 mode because the POWER7 mode is the highest mode supported by both POWER7 processor-based servers and POWER8 processor-based servers.
2. Migrate the logical partition from the POWER7 processor-based server to the POWER8 processor-based server.
3. Restart the logical partition on the POWER8 processor-based server. The hypervisor evaluates the configuration. The hypervisor does not set the current mode higher than the preferred mode. First, the hypervisor determines whether it can set the current mode to the preferred mode. If not, it then determines whether it can set the current mode to the next highest mode, and so on. In this case, the operating environment supports the POWER7 mode, so the hypervisor sets the current mode to the POWER7 mode.
4. Do not make any configuration changes to migrate the logical partition back to the POWER7 processor-based server because the POWER7 mode is supported on the POWER7 processor-based server.
5. Migrate the logical partition back to the POWER7 processor-based server.
6. Restart the logical partition on the POWER7 processor-based server. The hypervisor evaluates the configuration. The hypervisor determines that the operating environment supports the preferred mode of POWER7, and sets the current mode to the POWER7 mode.

Scenario: Migrating an inactive logical partition between servers with different processor types

The same logic from the previous scenarios applies to inactive partition mobility, except that the inactive partition mobility does not need the current processor compatibility mode of the logical partition because the logical partition is inactive. After you migrate an inactive logical partition to the destination server and activate that logical partition on the destination server, the hypervisor evaluates the configuration and sets the current mode for the logical partition similar to how the hypervisor sets the current mode for the logical partition when you restart a logical partition after active partition mobility. The hypervisor attempts to set the current mode to the preferred mode. If not, then it checks the next highest mode, and so on.