HP StorageWorks XP Remote Web Console Software - Manual (Page 30)

30 Overview of Continuous Access XP Journal
secondary array selects journal data S1 to be settled, because S1 is the lowest sequence number. When
S1 is removed from the sequence number queue, journal data S2 becomes the top entry, but it has not
arrived yet. Journal data S2’s management information is 0. The secondary array waits for journal data
S2. When journal data S2 arrives, the secondary array selects S2 as the next journal data to be settled.
The journal data that the secondary disk selects is marked as “host-dirty” and treated as formal data.
Figure 6 Selecting and settling journal at the secondary array
The secondary array settles and restores journal data to the secondary data volume as follows:
• Journal data stored in cache
Journal data is copied to the corresponding cached track and promoted to formal data.
• Journal data stored in the restore journal volume
Journal data is read from the restore journal volume to cache. Journal data that is read to cache is
copied to the existing cache track and promoted to formal data. After that, the space for the restore
journal volume is released.
Journal types
In addition to sending journal data for updating, the primary array sends control information to the
secondary array. This control information:
• Indicates volume pair status changes.
• Indicates when a primary array power-off sequence is initiated.
• 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 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