Scenarios: Using processor compatibility modes in partition mobility

Scenario: Migrating an active logical partition from a POWER8 processor-based server to a POWER9 processor-based server with firmware at level FW910

You want to migrate an active logical partition from a POWER8 processor-based server to a POWER9 processor-based server with firmware at level FW910, so that the logical partition can use the additional capabilities available with the POWER9 processor-based server with firmware at level FW910.

To migrate an active logical partition from a POWER8 processor-based server to a POWER9 processor-based server with firmware at level FW910, complete the following steps:

1. Set the preferred processor compatibility mode to the default mode. When you activate the logical partition on the POWER8 processor-based server, it runs in the POWER8 mode.
2. Migrate the logical partition to the POWER9 processor-based server with firmware at level FW910. 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 POWER9 processor-based server with firmware at level FW910. The hypervisor evaluates the configuration. Because the preferred mode is set to default and the logical partition now runs on a POWER9 processor-based server with firmware at level FW910, the highest mode available is the POWER9 Base mode. The hypervisor determines that the most fully-featured mode supported by the operating environment installed in the logical partition is the POWER9 Base mode and changes the current mode of the logical partition to the POWER9 Base mode.

Now, the current processor compatibility mode of the logical partition is the POWER9 Base mode and the logical partition runs on the POWER9 processor-based server with firmware at level FW910.

Scenario: Migrating the active logical partition back to the POWER8 processor-based server

A problem occurs and you need to migrate the active logical partition back to the POWER8 processor-based server. Because the logical partition now runs in the POWER9 Base mode and the POWER9 Base mode is not supported on the POWER8 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 POWER8 processor-based server.

To migrate the logical partition back to the POWER8 processor-based server, complete the following steps:

1. Change the preferred mode from the default mode to the POWER8 mode.
2. Restart the logical partition on the POWER9 processor-based server with firmware at level FW910. The hypervisor evaluates the configuration. Because the preferred mode is set to the POWER8 mode, the hypervisor does not set the current mode to a higher mode than the POWER8 mode. 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 POWER8 mode, so the hypervisor sets the current mode to the POWER8 mode.
3. Now that the logical partition runs in the POWER8 mode and the POWER8 mode is supported on the POWER8 processor-based server, migrate the logical partition back to the POWER8 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 POWER8 processor-based server and a POWER9 processor-based server with firmware at level FW910, 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 POWER8 mode because the POWER8 mode is the highest mode supported by both POWER8 processor-based servers and POWER9 processor-based server with firmware at level FW910.
2. Migrate the logical partition from the POWER8 processor-based server to the POWER9 processor-based server with firmware at level FW910.
3. Restart the logical partition on the POWER9 processor-based server with firmware at level FW910. 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 POWER8 mode, so the hypervisor sets the current mode to the POWER8 mode. Do not make any changes to the configured compatibility mode
4. Do not make any configuration changes to migrate the logical partition back to the POWER8 processor-based server because the POWER8 mode is supported on the POWER8 processor-based server.

   If the logical partition is restarted on the POWER9 processor-based server, the hypervisor re-evaluate the effective compatibility mode. Since the hypervisor cannot select an effective mode higher than the configured mode (POWER8 in this example), the logical partition remains in POWER8 effective mode.

5. Migrate the logical partition back to the POWER8 processor-based server.

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

The same rules 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 that is not possible, the hypervisor checks the next highest mode, and so on.