HP StorageWorks XP Remote Web Console Software - Manual (Page 80)

The utilization rate of the primary site in the 3DC cascading configuration rises compared with the
configuration which consists of only data volume as well as the operation of TrueCopy for Mainframe
Synchronous.
Basic Behavior
This section explains the basic behavior of a 3DC cascading configuration under the following
conditions:
•
The status of the TrueCopy for Mainframe Synchronous pair is Duplex. The status of the
Universal Replicator for Mainframe pair is also Duplex.
•
A host in the primary site issues an I/O request to the TrueCopy for Mainframe Synchronous
M-VOL
As illustrated in the following figure, if a host in the primary site issues an I/O request, data will
be stored into the TrueCopy for Mainframe Synchronous M-VOL. The data will also be stored into
the TrueCopy for Mainframe Synchronous R-VOL (that is, the Universal Replicator for Mainframe
primary data volume). After that, the fact that data has been stored will be reported to the primary
site, and then the fact that I/O has been finished will be reported to the host. Also, data in the
Universal Replicator for Mainframe primary data volume (that is, TrueCopy for Mainframe
Synchronous R-VOL) will be stored as journal data into the master journal volume in the intermediate
site. Sequence numbers, which indicate the order that data will be written, will be added to these
journal data. Also, journal data in the master journal volume in the intermediate site will be
transferred, independently from and asynchronously with the behavior mentioned above, to the
restore journal volume in the secondary site. Next, the journal data in the restore journal volume
will be restored to the Universal Replicator for Mainframe secondary data volume in the secondary
site; the journal data will be restored in the order of the sequence numbers that are added to
journal data. These sequence numbers ensure that updates to Universal Replicator for Mainframe
secondary data volumes in the secondary site will be made in the same order that updates to the
TrueCopy for Mainframe Synchronous M-VOL in the primary site are made.
As explained above, when the host in the primary site issues an I/O request to the TrueCopy for
Mainframe Synchronous M-VOL, the data will be restored asynchronously to the Universal Replicator
for Mainframe secondary data volume in the secondary site in a remote location.
Figure 33 Basic Behavior in a 3DC Cascading Configuration
If a TrueCopy for Mainframe Synchronous pair is suspended in a 3DC cascading configuration,
you will be able to resynchronize the pair by using differential copy. If a Universal Replicator for
Mainframe pair is suspended, you will be able to resynchronize the pair by using differential copy.
To perform disaster recovery from a failure in the primary site in a 3DC cascading configuration,
you must ensure that the fence level of the TrueCopy for Mainframe Synchronous M-VOL is Data
(CRIT=Y (ALL))). If this fence level is specified, you can perform disaster recovery by using the
Universal Replicator for Mainframe secondary data volume that contains the data stored in the
TrueCopy for Mainframe Synchronous M-VOL.
If the Universal Replicator for Mainframe pair status is Duplex or Pending and the TrueCopy for
Mainframe Synchronous pair in a 3DC cascading configuration is recovered, the DKC automatically
splits the Universal Replicator for Mainframe pair.
80 Preparing for Universal Replicator for Mainframe Operations