IBM XIV Storage System Copy Services and Migration

The following states or statuses are possible.► InitializingThe first step in remote mirroring is to create a copy of all the data from the master volumeor CG to the slave volume or CG. During this initial copy phase, the status remainsinitializing.► Synchronized (master volume or CG only)/consistent (slave volume or CG only)This status indicates that all data that has been written to the master volume or CG hasalso been written to the slave volume or CG. Ideally, the master and slave volumes or CGsmust always be synchronized. However, this does not always indicate that the twovolumes are absolutely identical in case of a disaster because there are situations whenthere might be a limited amount of data that was written to one volume, but that was notyet written to its peer volume. This means that the write operations have not yet beenacknowledged. These are also known as pending writes or data in flight.► Unsynchronized (master volume only)/inconsistent (slave volume only)After a volume or CG has completed the initializing stage and achieved the synchronizedstatus it can become unsynchronized (master) or inconsistent (slave). This occurs when itis not known whether all the data that has been written to the master volume has alsobeen written to the slave volume. This status can occur in the following cases:– The communications link is down and as a result certain data might have been writtento the master volume, but was not yet written to the slave volume.– Secondary XIV is down. This is similar to communication link errors because in thisstate, the Primary XIV is updated, whereas the secondary is not.– Remote mirroring is deactivated. As a result, certain data might have been written tothe master volume and not to the secondary volume.The XIV keeps track of the partitions that have been modified on the master volumes andwhen the link is operational again or the remote mirroring is reactivated. These changedpartitions can be sent to the remote XIV and applied to the slave volumes there.Asynchronous mirroring statesNote: This section only applies to asynchronous mirroring.The mirror states can be one of the following:► Inactive: The synchronization process is disabled. It is possible to delete a mirror.► Initializing: The initial copy is not done yet. Synchronization does not start until theinitialization completes.► When initialization is complete, the synchronization process is enabled. It is possible torun sync jobs and copy data between master and slave. The possible synchronizationstates are:– RPO_OK: Synchronization has completed within the specified sync job interval time(RPO).– RPO_Lagging: Synchronization has completed but took longer that the specifiedinterval time (RPO).Chapter 4. Remote Mirroring 81