Software Manual

is written to the primary data volume is obtained as an update journal. The update journal is copied
to the secondary storage system, and then restored to the secondary data volume.
The primary storage system obtains the update data that the host writes to the primary data volume
as update journals.
• Update journals are stored in journal volumes in the journal group of the primary data volume.
• Update journals that are copied to the secondary storage system are stored in journal volumes
in the journal group of the secondary data volume.
When the secondary storage system issues read journal commands, update journals are copied
from the primary storage system to the secondary storage system asynchronously with completion
of write I/Os by the host.
• The secondary storage system restores the journals updates to the secondary data volumes in
the order in which the write I/Os are made.
• Secondary data volumes are updated following the same process as the primary data volumes.
Journal Group Operations
XP Continuous Access Journal groups enable update sequence consistency to be maintained across
a journal group of volumes. The primary data volumes and secondary data volumes of the pairs
in a journal group must be located within one physical primary storage system and one physical
secondary storage system (1-to-1 requirement).
When more than one data volume is updated, the order in which the data volumes are updated
is managed within the journal group to which the data volumes belong. Consistency in data updates
is maintained among paired journal groups. XP Continuous Access Journal uses journal groups to
maintain data consistency among data volumes.
Journal Group Operations
XP Continuous Access Journal provides the following group-based operations to simplify and
expedite disaster or failure recovery procedures:
• Group operations at the primary storage system
Split all pairs in a journal group. See “Splitting a Pair of Data Volumes (Pairsplit-r)”
(page 189) for a description of the Group option.
◦
◦ Resume all suspended pairs in a journal group. See “Restoring a Mirror (Pairresync:
Resuming a Copy Operation)” (page 173) for a description of the XP Continuous Access
Journal Resume Range-Group pairresync option.
◦ Release all pairs in a journal group. See “Deleting Data Volumes from a Mirror (Pairsplit-S:
Ending a Copy Operation)” (page 174) for a description of the Delete Range-Group
pairsplit -S option.
• Group operations at the secondary storage system
Split (pairsplit-r) all pairs in a journal group. See “Splitting a Mirror (Pairsplit-r: Suspending
a Copy Operation)” (page 172) for a description of the Group option.
◦
◦ Release (pairsplit-S) all pairs in a journal group regardless of their consistency status. See
“Deleting Data Volumes from a Mirror (Pairsplit-S: Ending a Copy Operation)” (page 174)
for a description of the Delete Range-Group pairsplit-S option.
Read and Write I/O Operations During XP Continuous Access Journal Operations
Read / Read Failure
When a primary storage system receives a read I/O for an XP Continuous Access Journal primary
data volume, the primary storage system performs the read from the primary data volume. If the
read fails, the redundancy provided by the RAID1 or RAID5 technology recovers the failure. The
XP Continuous Access Journal Remote Copy Operations 23