Silicon Graphics InfiniteStorage 4000 Series, Configuring And Maintaining

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Chapter 7: Using the Asynchronous Mirroring Premium Feature 137

The original primary volumes are protected from new write requests just as if
they were secondary volumes.

A resynchronization process from the original primary volumes to the original
secondary volumes starts.
The resynchronization operation completes after all mirror-pairs of the asynchronous
mirror group are fully synchronized. If a scheduled synchronization operation is in
progress when a controller receives the role change request, the resynchronization
operation is stopped and restarted so that all regions flagged in both the host-write
tracking delta log and the synchronization delta log are copied to the secondary
volumes.
After the synchronization finishes and the roles are changed these actions take place:

Recovery points are created on the original primary storage array that has now
become the secondary storage array.

The volumes on the new primary storage array change state to Optimal and
operate normally: servicing read and write requests, tracking write requests, and
periodically synchronizing to the secondary volumes.
To change roles, use this form of the
set asyncMirrorGroup
command.
set asyncMirrorGroup [" asyncMirrorGroupName "]
role=(primary | secondary)
The
role
parameter enables you to define the role you want from either the primary
storage array or the secondary storage array. For example, if you are on the primary
storage array and you want to change roles, use the
secondary
parameter. The
command would look like this:
set asyncMirrorGroup [" asyncMirrorGroupName "]
role=secondary
As soon as you run this command, the storage arrays start changing roles.
Two optional parameters support changing the roles of the primary storage array and
the secondary storage array:
 force
 nosync
The
force
parameter forces a role change if the communications link between the
storage arrays is down and promotion or demotion on the local side results in a
dual-primary condition or a dual-secondary condition. To force a role reversal, set this
parameter to
TRUE
. The default value is
FALSE
.
The
nosync
parameter defines whether to perform an initial synchronization
between the primary storage array and the secondary storage array before a role
reversal operation is performed. To perform an initial synchronization, set this
parameter to
TRUE
. The default value is
FALSE
.