HP StorageWorks XP Remote Web Console Software - Manual (Page 19)

Initial Copy Operations
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/Os. Initial copy
operations are performed when you create a data volume pair 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 of 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 be 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 secondary 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 operation 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
Pair resync status to the status. Merging the difference bitmaps that are recorded on both primary
and secondary data volumes enables you to obtain the journal data for only 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.
The base-journal data of primary storage system is stored to the secondary storage system journal
volume according to the read command from the secondary storage system. After that, the
base-journal data is restored from the journal volume to the secondary data volume. The initial
copy operation will finish when all base-journals are restored.
If you manipulate volumes (not journal groups) to create or re-synchronize two or more data volume
pairs within the same journal group, the base journal of one of the pairs will be stored in the 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.
You can specify None as the copy mode for initial copy operations. If the None mode is selected,
initial copy operations will not be performed. The None mode must be used at your responsibility
only when you are sure that data in the primary data volume is completely the same as data in
the secondary data volumes.
When an RCU is shared with multiple MCUs, perform the pair resume operation after the system
option mode 593 is set to enabled (ON) if you resume 1025 or more pairs from multiple MCUs
(range: group) at the same time. Pair resume operations may fail if the system option mode 593
is not enabled (ON).
Update Copy Operation
When a host performs a write I/O operation to a primary data volume of a data volume pair, an
update copy operation will be performed. During an update copy operation, 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 update data that the host writes to the primary data volume
as update journals. Update journals will be stored in journal volumes in the journal group that the
primary data volume belongs to. 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
copied to the secondary storage system will be stored in journal volumes in the journal group that
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