HP XP Continuous Access Software - Manual (Page 34)

• Maintains sequence numbers in periods of low host activities.
Journal group operations
Journal groups maintain update sequence consistency across a group of journal volumes. The primary
and secondary data volumes of the pairs in a journal group must be located logically within one physical
primary array and one physical secondary array (1-to-1 requirement).
When more than one data volume is updated, the order in which data volumes are updated is managed
within the journal group to which the data volumes belong. Data update consistency is maintained
among paired journal groups. Continuous Access XP Journal uses journal groups to maintain data
consistency among data volumes.
Continuous Access XP Journal provides the following group-based operations to simplify and expedite
disaster or failure recovery procedures:
• Group operations at the primary array
• Split all pairs in a journal group. See
Splitting mirrors (Pairsplit-r: suspending copy operations)
for a description of the Suspend Range-Group pairsplit option.
• Resume all suspended pairs in a journal group. See Restoring mirrors (Pairresync: resuming
copy operations) for a description of the Resume Range-Group pairresync option.
• Delete all pairs in a journal group. See Deleting data volumes from mirrors (Pairsplit-S: ending
copy operations) for a description of the Delete Range-Group pairdelete option.
• Group operations at the secondary array
• Split (pairsplit-r) all pairs in a journal group. See
Splitting mirrors (Pairsplit-r: suspending copy
operations) for a description of the Suspend Range-Group pairsplit-r option.
• Delete (pairsplit-S) all pairs in a journal group regardless of their consistency status. See
Deleting data volumes from mirrors (Pairsplit-S: ending copy operations) for a description of
the Delete Range-Group pairsplit-S option.
Continuous Access XP Journal delta resync operations
When using Continuous Access XP Journal and Continuous Access XP Synchronous in a 3DC multi-target
configuration, Continuous Access XP Journal provides a delta resync operation between the two original
secondary sites as one of the solutions for failures in the primary site. In a 3DC multi-target configuration,
there is one primary site (DC1) and two secondary sites; Continuous Access XP Synchronous (DC2) and
Continuous Access XP Journal secondary sites (DC3). A dormant DC2-to-DC3 Continuous Access XP
Journal logical connection will only be invoked if DC1 becomes disabled. Under those circumstances, it
is desirable to uses a delta-update as opposed to a full copy in order to bring DC2 and DC3 into
synchronization. For more information, see Combining Continuous Access XP Journal with Continuous
Access XP Synchronous (3DC multi-target configuration) .
If a failure occurs on the primary site in a 3DC multi-target configuration, you must first use the RAID
Manager XP horctakeover command to begin using the Continuous Access XP Synchronous secondary
site (DC2) as the new primary site. If you perform a delta resync operation (between the two previous
secondary sites; DC2 and DC3) after the Continuous Access XP Synchronous secondary (DC2) site
becomes the primary site, a delta resync operation is able to quickly activate and sychnonize the
previously dormant DC2-to-DC3 Continuous Access XP Journal pair. Continuous Access XP Journal data
volumes are quickly synchronized between DC2 and DC3 and made available for use.
The delta resync operation consists of:
• Preparation before the failure occurs (see Journal obtain in Continuous Access XP Synchronous
secondary sites )
• Recovery after the failure occurs (see Switching Continuous Access XP's master journal group )
34 Overview of Continuous Access XP Journal