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

Primary host
Obtaining updated
journal data
Update copy
Write instruction
Secondar
y
host
Initial copy
Obtaining base-journal
Storage system
Storage system
Restore
Secondary
data
volume
Restore
journal
volume
Primary
data
volume
Master
journal
volume
Figure 5 Remote C opy Operations
This section describes the followi ng topics that are related to remote copy operations with Continuous
Access Journal:
•
Initial copy operation (see “Initial Copy Operation” on page 27),
•
Update co
py operation (see “Update Copy Operation”onpage28),
• Read and write I/O operations for Continuous Access Journal volumes (see
“Read and Write I/O Operations During Continuous Access Journal Operations” on page 29),
•
Secondary data volume write option (see “ Secondary Data Volume Write Option” on page 29),
•
Differe
ncemanagement(see“Difference Management”onpage29).
Initial Copy Operation
Initial copy operations synchronize data in the primary data volume and data in the secondary data
volume. Initial copy operations are performed independently from host I/O s. Initial copy operations
are per formed when you create a data volume pa ir or when you resynchronize a suspended pair.
The initial copy operation copies the base-journal data that is obtained from the primary data volume
at the
primary storage system to the secondary storage system, and then restores the base-journal to
the
secondary data volume.
If the journal obtain operation starts at the primary data volume, the primary storage system obtains
all
data in the primary data volume as the base-journal data, in sequence. The base-journal contains
a
replica of the entire data volume or a replica of updates to the data volume. The base-journal
will be copied from the primary storage system to the secondary storage system after the secondary
storage system issues a read-journal command. After a base-journal is copied to the secondary storage
system, the base-journal will b e stored in a restore journal volume in a restore journal group where the
secondary data volume belongs. After that, the data in the restore journal volume will be restored to
the
secondary data volume, so that the data in the secondar y data volume synchronizes with the data
in the primary data volume.
The base-journal data is stored in the entire data volume or the area for the difference. The area for
the
difference is used when the difference resynchronization o peration is performed. The journal data
for the entire data volume is created when the data volume pair is created. The difference journal data
is
obtained when the pair status of the data volume changes from the Suspending status to the Pair
resync status. Merging the difference bitmaps that are recorded on both primary and secondary data
volumes enables you to obtain the journal data for only the difference. When a data volume pair is
suspended, the status of data that is updated from the host to the primary and secondary data volumes
is
recorded to the difference bitmap.
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