Canceling A Pending Enhanced Global Mirror Group Role Change; Resolving Role Conflicts; Removing Logical Drives From The Enhanced Global Mirror Group - IBM System Storage DS3000 Programming Manual

If the role change is interrupted because of a communication failure between the storage subsystems, the
mirror roles can possibly end as two secondary roles. This role conflict does not compromise the data
synchronization state.

Canceling a pending Enhanced Global Mirror Group role change

You can cancel a pending role change by running this command:
stop enhancedGlobalMirrorGroup ["enhancedGlobalMirrorGroupName"] rolechange
This command restores the Enhanced Global Mirror Group to the normal operating state including write
requests to the logical drives on the primary logical drive. The synchronization process that was started
as part of the role change operation is allowed to finish. The next periodic resynchronization is scheduled
based on the most recently completed periodic synchronization and the current Enhanced Global Mirror
Group synchronization settings.

Resolving role conflicts

Because you can force a change in the role of the storage subsystems in an Enhanced Global Mirror
Group, sometimes this might result in a condition where you have two primary or two secondary roles at
the same time. This usually occurs when communications between the storage subsystems cannot take
place. For example, the original primary side might be operational, but cannot be reached because of a
link failure. In this case, a forced promotion of the secondary to become a primary results in both sides
being able to receive new data write requests after the most recent resynchronization. Later, the original
primary site might be reactivated or connectivity reestablished resulting in both local and remote storage
subsystems viewing themselves as the primary.
If you have a role conflict, your Enhanced Global Mirror Group might have two primary logical drives or
two secondary logical drives in an Enhanced Global Mirror Group. If you have two primary logical
drives, both logical drives can accept host writes, but you do not have any mirror logical drives. If you
have two secondary logical drives, neither logical drive can accept host writes. In either case, the user no
longer has a valid Enhanced Global Mirror Group.
If such a role conflict occurs, you need to migrate the mirrored pair back to a state in which one side is
clearly recognized as primary and the other as secondary. To migrate back to a valid Enhanced Global
Mirror Group, use this command.
set enhancedGlobalMirrorGroup ["enhancedGlobalMirrorGroupName"] role=(primary | secondary)
Run this command on one of the storage subsystems in the Enhanced Global Mirror Group and define
the role of that storage subsystem as you need to meet your mirroring requirements. Define the storage
subsystem as either the storage subsystem with the primary logical drives or the storage subsystem with
the secondary logical drives.

Removing logical drives from the Enhanced Global Mirror group

When you have an Enhanced Global Mirror Group you have three logical drives that you need to
manage:
v Primary on the local storage subsystem
v Secondary on the remote storage subsystem
v Repository on both storage subsystems
Use the remove logicalDrive enhancedGlobalMirrorGroup command to remove the link between a
primary logical drive and a secondary logical drive.
Removing a logical drive from an Enhanced Global Mirror Group disassociates the logical drive from the
Enhanced Global Mirror Group and also disassociates the corresponding logical drive on the remote
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Chapter 7. About Enhanced Global Mirroring premium feature