HP StorageWorks XP24000 Continuous Access Journal Software User and Reference Guide, v01 (T5278-96001, June 2007)

The base-journal d ata of the primary storage system is stored in the secondar y storage system journal
volume according to the read command from the secondar y storage system. After that, the base-journal
data is restore d from the journal volume to the secondary d ata volume. The initial copy operation
will finish when all base-journals are restored.
Note: If you manipu late volumes (not journal groups) to create or resynchronize two or m ore data volume
pairs within thesamejournal group, thebasejournal of oneofthe pairswillbestoredinthe restore
journal volume, and then the base journal of another pair will be stored in the restore journal volume.
Therefore, the operation for restoring the latter base journal will be delayed.
Note: You can specify None as the copy mode for initial copy operations. If the None m o d e is selected,
initial copy operations will not be performed. You are responsible for using the None mode only when
you are sure that data in the primary data volume is completely the same as data in the secondary
data volumes.
Update Copy Operation
When a host per forms a write I/O operation to the primary data volume of a data volume pair, an
update
copy operation will be performed. During an update copy o peration, the update data that is
written to
the primary data volume is obtained as an update journal. The update journal will be 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
jou
rnals. Update journals will be stored in journal volumes in the journal group to which the
primary data volume belongs. When the secondary storage system issues read journal commands,
update
journals will be copied from the primary storage system to the secondary storage system
asynchronously with completion of write I/Os by the host. Update journals that are co pied to the
secondary storage system will be stored in journal volumes in the journal group to which the secondary
data volu
me
belongs. The secondary storage system will restore the update journals to the secondary
data vol
umes in the order write I/Os were ma de, so that the secondary data volumes will be updated
just like the primary data volumes are updated.
Journal Group Operations
Continuous Access Journal journal groups enable update sequence consistency to be maintained across
a
journal group of volumes. The primary data volumes and secondar y data volumes of the pairs in a
journal group must be lo cated within one p hysical primary storage system and one physical secondar y
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. Continuous Access Journal uses journal groups to maintain
data consistency among data volumes.
Journal Group Operations
Continuous Access Journal provides the following group-based operations to simplif y and expedite
disaster or failure recovery procedures:
• Grou
p
operations at the primary storage system
• Split all pairs in a journal group. See
“Splitting a Mirror (Pairsplit-r: Suspending a Copy Operation)” on page 122 for a description
of the Suspend Range-Group pairsplit option.
• Resume all suspended pairs in a journal group. See
“Restoring a Mirror (Pairresync: Resuming a Copy Operation)” on page 123 for a description
of the Continuous Access Jou rnal Resume Range-Group pairresync option.
•Re
lease
all pairs in a journal group. See
“
Deleting Data Volumes from a Mirror (Pairsplit-S: Ending a Copy O peration)” on page 1 24
f
or a
description of the Delete Range-Group pairsplit -S op tion.
• Group operations at the secondary storage system
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About
Continuous Access Journal Operations