HP StorageWorks XP Remote Web Console Software - Manual (Page 29)

NOTE: When you issue the DEVSERV command to the Universal Replicator for Mainframe
secondary data volume, INDETERMINATE FAILING UNIT is returned, if the status of Universal
Replicator for Mainframe secondary data volume is online. INTERVENTION REQUIRED is returned,
if the status of Universal Replicator for Mainframe secondary data volume is offline.
Secondary Data Volume Write Option
For additional flexibility, Universal Replicator for Mainframe provides a secondary data volume
write option (S-Vol. Write) which enables write I/O to the secondary data volume of a split Universal
Replicator for Mainframe pair. The secondary data volume write option can be selected by the
user during the Suspend Pair operation and applies only to the selected pair(s). The secondary
data volume write option can be accessed only when you are connected to the primary storage
system. When you resync a split Universal Replicator for Mainframe pair which has the secondary
data volume write option enabled, the secondary storage system sends the secondary data volume
track bitmap to the primary storage system, and the primary storage system merges the primary
data volume and secondary data volume bitmaps to determine which tracks are out-of sync. This
ensures proper resynchronization of the pair.
Secondary Data Volume Read Option
For additional flexibility, Universal Replicator for Mainframe offers a special secondary data volume
read option. The HP representative enables the secondary data volume read option on the secondary
storage system (mode 20). The secondary data volume read option allows you to read a Universal
Replicator for Mainframe secondary data volume only while the pair is suspended, that is, without
having to release the pair. The secondary storage system will allow you to change only the VOLSER
of the suspended secondary data volume, so that the secondary data volume can be online to the
same host as the primary data volume while the pair is suspended. All other write I/Os will be
rejected by the secondary storage system. The primary storage system copies the VOLSER of the
primary data volume back onto the secondary data volume when the pair is resumed. When the
secondary data volume read option is not enabled and/or the pair is not suspended, the secondary
storage system rejects all read and write I/Os to a Universal Replicator for Mainframe secondary
data volume.
NOTE: All the I/Os to a Universal Replicator for Mainframe secondary data volume will be
rejected while the volume is being deleted. For example, even though the suspended Universal
Replicator for Mainframe secondary data volume accepts read and write I/Os, if you delete the
volume, the secondary storage system rejects all read and write I/Os that were once accepted.
Difference Management
The differential data (updated by write I/Os during a split or suspension) between the primary
data volume and the secondary data volume is stored in each track bitmap. When a split/suspended
pair is resumed (Resume Pair), the primary storage system merges the primary data volume and
secondary data volume bitmaps, and the differential data is copied to the secondary data volume.
NOTE: The number of bitmap areas affects the maximum possible number of pairs that can be
created in the storage system. For details on the maximum possible number of pairs, see “The
Maximum Number of Pairs” (page 53) .
Journal Processing
The Universal Replicator for Mainframe journal data contains the primary data volume updates
and the metadata information (associated control information), which enables the secondary storage
Journal Processing 29