Fallover and fallback

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PowerHA® SystemMirror® Enterprise Edition for Metro Mirror handles the automation of fallover from one site to another in response to an outage at a production site, minimizing recovery time. When a site fails, the resource group configuration determines whether source volumes are accessible from the secondary site.

PowerHA SystemMirror automates application recovery by managing replicated resources defined to PowerHA SystemMirror resource groups in the following manner:

  • The fallover of nodes within a site based on node priority (as identified in the nodelist for a resource group)
  • The fallover between sites (as specified by the site management policy for a resource group)
  • The fallback of a resource group or site as configured.

When an application is running on an active production site:

  • Updates to the application data are made to the disks associated with the active production site.
  • Data is mirrored using PPRC to the backup disks.

If the node or the disks at the production site become unavailable:

  • The application moves to a server at the backup site.
  • The application continues operation using the mirrored copy of the data.

When the initial production site becomes active again, resource group and site management policies determine whether or not the application moves back to the previous site:

  • The direction of mirroring may be reversed.
  • The application may be stopped and restarted on another node.
  • Manual intervention may be required to bring the application back to a nominal functioning state.