Chapter 10. Copy services 583
ConsistentSynchronized
ConsistentSynchronized is a connected state. In this state, the master volume is accessible
for read and write I/O, and the auxiliary volume is accessible for read-only I/O. Writes that are
sent to the master volume are also sent to the auxiliary volume. Either successful completion
must be received for both writes, the write must be failed to the host, or a state must transition
out of the ConsistentSynchronized state before a write is completed to the host.
A stop command takes the relationship to the ConsistentStopped state. A stop command
with the -access parameter takes the relationship to the Idling state.
A switch command leaves the relationship in the ConsistentSynchronized state, but it
reverses the master and auxiliary roles (it switches the direction of replicating data). A start
command is accepted, but has no effect.
If the relationship or Consistency Group becomes disconnected, the same transitions are
made as for ConsistentStopped.
Idling
Idling is a connected state. Both master and auxiliary volumes operate in the master role.
Therefore, both master and auxiliary volumes are accessible for write I/O.
In this state, the relationship or Consistency Group accepts a start command. MM/GM
maintains a record of regions on each disk that received write I/O while they were idling. This
record is used to determine what areas must be copied following a start command.
The start command must specify the new copy direction. A start command can cause a
loss of consistency if either volume in any relationship received write I/O, which is indicated by
the Synchronized status. If the start command leads to loss of consistency, you must specify
the -force parameter.
Following a start command, the relationship or Consistency Group transitions to
ConsistentSynchronized if there is no loss of consistency, or to InconsistentCopying if there
is a loss of consistency.
Also, the relationship or Consistency Group accepts a -clean option on the start command
while in this state. If the relationship or Consistency Group becomes disconnected, both sides
change their state to IdlingDisconnected.
IdlingDisconnected
IdlingDisconnected is a disconnected state. The target volumes in this half of the
relationship or Consistency Group are all in the master role and accept read or write I/O.
The priority in this state is to recover the link to restore the relationship or consistency.
No configuration activity is possible (except for deletes or stops) until the relationship
becomes connected again. At that point, the relationship transitions to a connected state. The
exact connected state that is entered depends on the state of the other half of the relationship
or Consistency Group, which depends on the following factors:
The state when it became disconnected
The write activity since it was disconnected
The configuration activity since it was disconnected
If both halves are IdlingDisconnected, the relationship becomes Idling when it is
reconnected.
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