Sun Microsystems StorageTek 6140 Administration Manual page 106

Caution: If I/O operations to the primary and secondary volumes occur during a
role reversal, data is lost when you initiate a synchronization operation. The current
secondary volume is brought into synchronization with the current primary volume,
and any writes that have been written to the secondary volume are lost.
Secondary to Primary
You usually promote a secondary volume to a primary volume in a replication set
when a catastrophic failure has occurred on the array that contains the primary
volume. You need to promote the secondary volume so that host applications that
are mapped to the primary volume can still access data and so that business
operations can continue. If the replication set is operating normally with a viable
link, promoting the secondary volume to the primary volume automatically demotes
the primary volume to the secondary volume.
When the secondary volume becomes a primary volume, any hosts that are mapped
to the volume through a volume-to-LUN mapping will now be able to read or write
to the volume. If a communication problem between the secondary and primary
sites prevents the demotion of the primary volume, an error message is displayed.
However, you are given the opportunity to proceed with the promotion of the
secondary volume, even though this will lead to a dual-primary condition.
To promote a secondary volume to a primary volume, see "Reversing Roles" on
page 102.
Primary to Secondary
You can demote a primary volume to a secondary role during normal operating
conditions. If the replication set is operating normally with a viable link, demoting
the primary volume to the secondary volume automatically promotes the secondary
volume to the primary volume.
When the secondary volume becomes a primary volume, any host that accesses the
primary volume through a volume-to-LUN mapping will no longer be able to write
to the volume. When the primary volume becomes a secondary volume, only remote
writes initiated by the primary controller will be written to the volume. If a
communication problem between the primary and secondary sites prevents the
promotion of the secondary volume, an error message is displayed. However, you
are given the opportunity to proceed with the demotion of the primary volume,
even though this will lead to a dual-secondary condition.
To demote a primary volume to a secondary volume, see "Reversing Roles" on
page 102.
Note: To correct a dual-primary or dual-secondary condition, you must delete the
replication set and then create a new one.
90 Sun StorageTek Array Administration Guide • May 2006