Entries in the /etc/horcm.conf file for Hitachi Universal Replicator device groups can associate journal volumes with data LUNs. Journal volumes are specially configured LUNs on the storage system array. On both the primary and secondary arrays, local journal volumes store data that has been written to application data storage on the primary cluster, but not yet replicated to application data storage on the secondary cluster. Journal volumes thereby enable Hitachi Universal Replicator to maintain the consistency of data even if the connection between the paired clusters in a Sun Cluster Geographic Edition partnership temporarily fails. A journal volume can be used by more than one device group on the local cluster, but typically is assigned to just one device group. Hitachi TrueCopy does not support journaling.
If you want to implement journaling, you must configure Hitachi Universal Replicator device groups as properties of the HORCM_LDEV parameter because only that parameter supports the association of data LUNs with journal volumes in the Sun Cluster Geographic Edition Hitachi Universal Replicator module. If you configure Hitachi Universal Replicator device groups by using the HORCM_DEV parameter, no journaling occurs, and Hitachi Universal Replicator has no greater functionality than does Hitachi TrueCopy.