HP XP Continuous Access Software - Manual (Page 24)

Journal volumes
When using Continuous Access XP Journal, updates to primary data volumes are stored in other volumes,
which are called journal volumes. Updates (which are sometimes referred to as update data) that are
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 and secondary arrays temporarily fails, remote copy operations continue after
the communications path is recovered.
Because journal volumes can contain more update data than cache memory can contain, remote copy
operations can continue if data transfers from hosts to the primary array are faster than data transfers
between the primary and secondary arrays for a relatively long time period.
Number of journal volumes
One journal group can contain up to 16 journal volumes. Each journal volume can have different volume
sizes and RAID configurations. Journal data entries are stored sequentially and separately in each
journal volume in the same journal group.
Journal volume specifications
• Logical unit (LU) types
The following DKU emulation types are allowed for journal volumes.
Table 2 Emulation types for journal volumes
Emulation category Supported emulation types
DKU (drive) OPEN-V
NOTE:
You can only use OPEN-V volumes for journal volumes.
• Volumes and capacities
You can use custom volumes for journal volumes.
Journal volumes in the same journal group can have different capacities. A master journal volume and
the corresponding restore journal volume can have different capacities.
A journal volume consists of two areas: one is used to store journal data, and the other is used
to store metadata for remote copy.
• RAID configurations
Journal volumes support all RAID configurations that the local array supports. Journal volumes also
support all physical volumes that the local array supports.
Volumes in parity groups with a RAID-5 (7D+1P) configuration are usually used as journal volumes.
• Support for optional programs
You can use Cache LUN XP volumes for journal volumes.
CAUTION:
You cannot use volumes containing a volume management area (VMA) as journal volumes. For more
information, see the HP StorageWorks LUN Security XP Extension user guide.
Journal volume restrictions
• Registering journal volumes
24 Overview of Continuous Access XP Journal