HP StorageWorks XP Remote Web Console Software - Manual (Page 74)

consistency group, pairs can be deleted. If you delete the following pairs, the specified split
time will be deleted:
◦ Delete all the SIz pairs belonging to the ShadowImage for z/OS consistency group.
◦ Delete all the URz pairs belonging to the URz restore journal group.
Combining URz with TCz Synchronous (3DC Cascading Configuration)
The XP storage system provides the function to combine URz and TCz Synchronous. This combination
is intended to ensure that the response time against host I/Os is comparable, regardless of whether
the distance between the primary and the secondary sites are short or long. This combination is
also intended to ensure that the secondary site stores data that has been stored in the primary site
even when a failure occurs in the primary site. These intentions will be fulfilled if remote copy
operations are performed using cascading connections and a three data center (3DC) configuration;
in a 3DC configuration, an intermediate site is located between the primary and secondary sites.
Figure 35 (page 74) shows an example of a 3DC cascading configuration in which URz and TCz
Synchronous are combined. In this configuration, the volume in the primary site is a TCz Synchronous
main volume (M-VOL). The corresponding TCz Synchronous remote volume (secondary data volume)
is the volume in the intermediate site, which is within a short distance from the primary site. This
TCz Synchronous remote volume is also used as a URz primary data volume. The corresponding
URz secondary data volume is the volume in the secondary site, which is within a long distance
from the intermediate site. If a host issues an I/O to the TCz Synchronous main volume in the
primary site, data will be transferred via TCz Synchronous and URz to the secondary site and will
be restored to the secondary data volume.
Figure 35 3DC Cascading Configuration (Combining URz with TCz)
Data that is copied by TCz Synchronous is stored in the URz primary data volume. If a failure
occurs at the TCz Synchronous M-VOL, business tasks can continue by using data in the URz
secondary data volume containing data in the TCz Synchronous M-VOL. Data in the TCz
Synchronous M-VOL is restored via URz to the secondary data volume in the secondary site, with
update sequence integrity ensured. If a failure occurs at both TCz Synchronous M-VOL and
secondary data volume due to a disaster or some other reason, disaster recovery can be performed
using the URz secondary data volume.
A TCz Synchronous M-VOL must be created in an XP storage system. The fence level of the TCz
Synchronous M-VOL must be Data (CRIT=Y (ALL)).
Basic Behavior
This section explains the basic behavior of a 3DC cascading configuration under the following
conditions:
•
The status of the TCz Synchronous pair is Duplex. The status of the URz pair is also Duplex.
•
A host in the primary site issues an I/O request to the TCz Synchronous M-VOL
As illustrated in Figure 36 (page 75) , if a host in the primary site issues an I/O request, data will
be stored into the TCz Synchronous M-VOL. The data will also be stored into the TCz Synchronous
R-VOL (that is, the URz primary data volume). After that, the fact that data has been stored will be
74 Requirements and Restrictions for Universal Replicator z/OS Operations