Modifying the topology of a Global Mirror session

Complete this task to modify the topology of a Global Mirror session that is not part of a script.

About this task

A Global Mirror session consists of tuning parameters and topology, both of which can be modified. However, they cannot be modified using the same method. The modification of the Global Mirror topology requires that you stop the Global Mirror session, change the topology, and then restart Global Mirror processing. The modification of the tuning parameters is managed differently.

Topology in this process refers to the list of subordinate storage servers. You establish remote mirror and copy paths between the master and subordinate LSSs. Just one LSS per subordinate server is sufficient. When you define the remote mirror and copy path, you identify the primary LSS on the master server. The secondary LSS in the remote mirror and copy path establishes command points to a corresponding subordinate server. These LSSs are part of the topology specification that defines the communication paths between the master and subordinate storage servers.

Note: When you restart Global Mirror processing, the tuning parameters revert to their DS CLI default values.

Complete the following steps to modify the topology of a Global Mirror session. The example commands in this task are shown in two formats. The first format shows the type of information that the command requires. The second format provides the command with declared values for the variables.

Procedure

Issue the showgmir command to display a detailed properties or performance metrics report for a Global Mirror logical subsystem ID. Enter the showgmir command at the dscli command prompt with the following parameters and variables:
For a detailed properties report: dscli> showgmir -dev storage_image_ID -fullid LSS_ID

For a performance metrics report: dscli> showgmir -dev storage_image_ID -metrics LSS_ID
These commands are entered as follows when you add values:
```
dscli> showgmir -dev IBM.2107-75FA120 -fullid 10
```
```
dscli> showgmir -dev IBM.2107-75FA120 -metrics 10
```
Use the report as a guide to see what is currently being processed and to determine what topology values you want to change.
Issue the rmgmir command to stop Global Mirror processing. Enter the rmgmir command at the dscli command prompt with the following parameters and variables:
dscli> rmgmir -dev storage_image_ID -lss ID -session session_ID
Master_Control_Path_LSS_ID:Subordinate_Control_Path_LSS_ID

Example
```
dscli> rmgmir -dev IBM.2107-75FA120 -lss 10 
-session 01 IBM.2107-75FA120/00:IBM.2107-75FA150/00
```
Notes:
1. This command can interrupt the formation of a consistency group. If this command does not complete, an error code is issued. If this occurs, examine the error code and follow your local procedures for problem determination. In most cases, if you correct the error, you can successfully reissue the rmgmir command. If, however, the reissued rmgmir command fails and Global Mirror processing must be stopped, reissue the rmgmir command with the -force parameter.
2. You cannot use the rmgmir command to stop a script that involves Global Mirror processing. The only way to stop a script is to press the Ctrl C keys on your keyboard. This action stops the DS CLI session. However, it does not stop the microcode that is processing Global Mirror transactions. To stop the microcode processing, you must log back in to the DS CLI session and issue the rmgmir command.
Enter Y to confirm that you want to stop Global Mirror processing for the specified session.
The message is displayed as follows:
```
Are you sure you want to stop Session ID (xx)? [y/n]: Y
Global Mirror for Session ID 01 successfully stopped.
```
Issue the mkgmir command with your updated master and subordinate LSS changes to start Global Mirror processing. Enter the mkgmir command at the dscli command prompt with the following parameters and variables:
dscli> mkgmir -dev storage_image_ID -lss ID -session session_ID
-cginterval seconds -coordinate milliseconds -drain seconds
Master_Control_Path_LSS_ID:Subordinate_Control_Path_LSS_ID

Example
```
dscli> mkgmir -dev IBM.2107-75FA120 -lss 10 -session 01 -cginterval 0
-coordinate 40
-drain 35 IBM.2107-75FA120/00:IBM.2107-75FA150/00
```
Notes:
1. You can change your mind and decide not to change any of the topology values. However, you must still issue the mkgmir command to resume Global Mirror processing after you have stopped the processing. Because the resumegmir command is used only with the pausegmir command, you cannot issue the resumegmir command to restart the processing.
2. When you stopped the Global Mirror session, the values for the tuning parameters become invalid. You must specify values for these parameters (-cginterval, -coordinate, -drain) when you restart your Global Mirror session.