Modifying the tuning parameters of a Global Mirror session

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Complete this task to modify the tuning parameters of a Global Mirror session.

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 tuning parameters requires that you pause the Global Mirror session and change the parameters. Then you can resume the session with the new tuning parameter values. The modification of the Global Mirror topology requires that you stop the Global Mirror session, change the topology, and then restart Global Mirror processing.

A Global Mirror session includes the following tuning parameters:
  • Consistency group interval time
  • Maximum coordination interval time
  • Maximum consistency drain time
There are two specific occasions when you might want to modify the tuning parameters:
  • After the initial setup of your session and your analysis of Global Mirror processing indicates that these parameters should be adjusted.
  • After you have stopped (not just paused) Global Mirror processing. When you restart Global Mirror processing, the values for the tuning parameters revert to their DS CLI default values.

Complete the following steps to modify the tuning parameters of a Global Mirror session. The example commands that are displayed 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

  1. Issue the pausegmir command to pause Global Mirror processing on the specified logical subsystem and the specified session within the logical subsystem. Enter the pausegmir command at the dscli command prompt using the following parameters and variables:

    dscli> pausegmir -dev storage_image_ID -lss LSS_ID -session session_ID Master_Control_Path_LSS_ID:Subordinate_Control_Path_LSS_ID

    Example

    dscli> pausegmir -dev IBM.2107-75FA120 -lss 10 
-session 01 IBM.2107-75FA120/00:IBM.2107-75FA150/00

    A confirmation message indicates that the session has been paused after all buffered write operations to the target have been processed.

  2. Issue the showgmir command to receive a report that provides the current properties or performance metrics 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 LSS_ID

    For a performance metrics report: dscli> showgmir -dev storage_image_ID -metrics LSS_ID

    Example

    These commands are entered as follows when you add values:
    dscli> showgmir -dev IBM.2107-75FA120 10
    dscli> showgmir -dev IBM.2107-75FA120 -metrics 10
  3. Analyze the report and determine which if any of the Global Mirror tuning parameters must be changed.
  4. Issue the resumegmir command with the values for all three tuning parameters. Enter the resumegmir command at the dscli command prompt with the following parameters and variables:

    dscli> resumegmir -dev storage_image_ID -lss ID -cginterval seconds
    -coordinate milliseconds -drain seconds -session session_ID
    Master_Control_Path_LSS_ID:Subordinate_Control_Path_LSS_ID

    Example

    The example command shows all three tuning parameters with new values. You must specify a value for all three tuning parameters even if only one value has changed. The values for the two unchanged tuning parameters would be the DS CLI default values.

    dscli> resumegmir -dev IBM.2107-75FA120 -lss 10 -cginterval 10 
-coordinate 60 -drain 35 -session 01 
IBM.2107-75FA120/00:IBM.2107-75FA150/00
    Notes:
    1. The -cginterval parameter specifies the consistency group interval time, in seconds. The value specifies how long to wait between the formation of consistency groups. If this value is set to zero, consistency groups are formed continuously. The DS CLI default value is 0.
    2. The -coordinate parameter specifies the maximum coordination interval, in milliseconds. This value indicates the maximum time that Global Mirror processing queues Primary/Host/IO to start forming a consistency group. The DS CLI default value is 50 milliseconds.
    3. The -drain parameter specifies the maximum amount of time that writes (in seconds) are inhibited to the remote site before the current consistency group must stop. The DS CLI default value is 30 seconds.