HP StorageWorks XP Remote Web Console Software - Manual (Page 18)

Caution: Data volumes and journal volumes that belong to different LDKCs cannot coexist in a
journal group.
For detailed information about the specification of journal groups, see “Journal Group Specifications”
(page 48) .
Data Volume Pairs
XP Continuous Access Journal performs remote copy operations for data volume pairs created by
the user. Each XP Continuous Access Journal pair consists of one primary data volume and one
secondary data volume, which can be located in different storage systems. The XP Continuous
Access Journal primary data volumes are the primary volumes (LUs) that contain the original data,
and the XP Continuous Access Journal secondary data volumes are the secondary volumes (LUs)
that contain the backup or duplicate data. During normal XP Continuous Access Journal operations,
the primary data volume remains available to all hosts at all times for read and write I/O operations.
During normal XP Continuous Access Journal operations, the secondary storage system rejects all
host-requested write I/Os for the secondary data volume. The secondary data volume write enable
option allows write access to a secondary data volume while the pair is split, and uses the secondary
data volume and primary data volume track maps to resynchronize the pair (see
“Secondary Data
Volume Write Option” (page 24) ).
XP Continuous Access Journal also supports LUN Expansion (LUSE), Virtual LVI/LUN (VLL), and
Cache Residency Manager features, so that XP Continuous Access Journal meets a variety of user
needs and facilitates data copying and data migration. This ensures that all user data can be
backed up or duplicated. See
“Logical Unit (LU) Types” (page 45) for further information on LU
requirements and support.
Journal Volumes
When XP Continuous Access Journal is used, updates to primary data volumes can be stored in
other volumes, which are called journal volumes. The updates (which are sometimes referred to
as update data) stored in journal volumes are called journal data.
Because journal data is stored in journal volumes, you can perform and manage highly reliable
remote copy operations without suspension of remote copy operations. For example, Even if a
communications path between the primary storage system and the secondary storage system fails
temporarily, remote copy operations can continue after the communications path is recovered.
Usually, the speed of data transfer (that is, the amount of data that is transferred in a period of
time) between the primary and the secondary storage system is the same or faster than the speed
of data transfer between the host and the primary storage system. Since journal volumes can
contain more update data than cache memory, even when the speed of data transfer between the
host and the primary storage system temporarily exceeds the speed of data transfer between the
primary storage system and the secondary storage system, the storage systems can continue the
remote copy operation without interruption for a longer time compared to the program product
that stores the update data in cache memory.
Number of Journal Volumes
One journal group can contain up to 64 journal volumes. Each of the journal volumes can have
different volume sizes and different RAID configurations. Journal data is stored sequentially and
separately into each journal volume in the same journal group.
Specifications for Journal Volumes
•
Types of logical units (LUs):
The following DKU emulation types are allowed for journal volumes:
18 About XP Continuous Access Journal Operations