Restarting an AIX Host System that is enabled for Open HyperSwap

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When an AIX® host system is restarted, the host automatically opens any volumes for I/O that were open before the system was restarted. If Open HyperSwap® was enabled for a set of volumes on the host system, the host must determine which storage system is the primary system before the host can allow the volumes to be opened.

If the Metro Mirror relationship for the set of volumes is in Prepared or Suspended state and the host has connectivity to both the primary and secondary storage systems, the host can determine through the hardware which storage system is the primary system. In this situation, the host automatically opens the volumes.

If the Metro Mirror relationship for the set of volumes is in Prepared state and the host has connectivity to only the secondary storage system, all I/O to the volumes might be blocked on the host system. The I/O might be blocked until the host can verify the primary volume in the relationship. The AIX varyonvg command fails to open the volumes for I/O to prevent the application from writing to an incorrect volume. If the host can determine which volume is the primary volume in the relationship and connectivity to the primary storage system is still lost, a Hyperswap event is triggered. This event causes all I/O to be automatically opened and directed to the secondary storage system.

If the Metro Mirror relationship for the set of volumes is in Target Available state or the host system does not have connectivity and is unable to determine which site is the primary site, all I/O to the volumes are blocked on the host system. The Target Available state occurs after a Hyperswap or a Recover command is issued for the session. The varyonvg command fails to open the volumes for I/O to prevent the application from writing to an incorrect volume.

Unblocking I/O on the host system after a host system restart

When any of the previous scenarios cause I/O to be blocked, manual actions might be necessary to remove the block.

If the relationships are in Target Available state on the hardware, issue the Start command to the session in the required direction of the relationship. This action defines the primary storage system for the host. The host system can allow the volumes to be opened for I/O processing.

If the relationships cannot be restarted, or the host cannot determine the primary storage system, it might be necessary to manually decouple the volumes on the host system.

To decouple the volumes, complete one of the following tasks:
  • Stop the session or remove the copy set. This action requires a full copy when the relationships are restarted.
  • Remove Object Data Manager (ODM) entries by using the following command: 
    odmdelete -o Volume_Equivalency
    Restriction: This command deletes copy set information; use it only for this scenario.