Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access XP P9000 for Linux B.01.00.00

(I/O ordering). A CT group is equal to a device group in the Raid Manager configuration file. A
consistency group ID (CTGID) is assigned automatically during pair creation.
NOTE: Different P9000 and XP models support different maximum numbers of Consistency
Groups. For details, see the P9000 user guide or XP user guide.
Limitations of asynchronous mode
The following are restrictions for an asynchronous CT group in a Raid Manager configuration file:
• Asynchronous device groups cannot be defined to extend across multiple XP Series disk arrays.
• When making paired volumes, the Raid Manager registers a CTGID to the XP Series disk
array automatically at paircreate time, and the device group in the configuration file is
mapped to a CTGID. Efforts to create a CTGID with a higher number ends with the return
value EX_ENOCTG.
• Metrocluster supports only one consistency group per package.
Furthermore, the number of packages that can be configured to use a consistency group is limited
by the maximum number of consistency groups that are supported by the XP model in the
configuration or the maximum number of packages in the cluster (whichever is smaller).
Continuous Access journal overview
Continuous Access Journal is an asynchronous data replication between two XP or P9000 storage
disk arrays. Continuous Access Journal uses two main features, disk-based journaling and pull-style
replication. These two features reduce internal cache memory consumption, while maintaining
performance and operational resilience.
Journal volume
When Continuous Access Journal is used, updates to PVOL can be stored in other volumes, which
are called journal volumes. The update data that is stored in journal volumes is called journal data.
The journal volumes are architected and optimized for keeping large amounts of host-write data
in sequence.
When collecting the data to be replicated, the primary XP or P9000 array writes the designated
records to a special set of journal volumes. The remote storage array then reads the records from
the journal volumes, pulling them across the communication link and thus reducing resource
consumption on the primary storage system as shown in Figure 2 (page 9).
8 Introduction