HP XP Continuous Access Software - Manual (Page 15)

Journal volumes
When using XP Continuous Access 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
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Logical unit (LU) types
The following DKU emulation types are allowed for journal volumes.
Table 1 Emulation types for journal volumes
Supported emulation types Emulation category
OPEN-V
You can only use OPEN-V volumes
for journal volumes. DKU (drive)
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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.
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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.
Components 15