HP XP Continuous Access Software - Manual (Page 54)

The following factors affect the speed of writing to and reading from journal volumes, particularly
when a temporary communications path failure occurs between the primary and the secondary
arrays or when the amount of data transferred from hosts to the primary array increases:
•
RAID configuration of the RAID groups that will contain journal volumes
•
Types of physical volumes in the RAID groups that will contain journal volumes
•
Frequency of access to non-journal volumes in the RAID groups that will contain journal volumes
•
Data transfer speed required for the non-journal volumes
•
Disk usage rate for RAID groups
The journal volumes' capacity affects the time during which data transfer with hosts can continue
without being influenced by a temporary communications path failure between the primary and
secondary arrays or an increase in the data to be transferred from hosts to the primary array.
Planning process
Data transfer speed required for journal volumes
Figure 13 (page 54) illustrates how the data transfer speed (that is, the amount of data to be
transferred per unit of time) changes as time elapses, showing different types of data transfer
speeds with XP Continuous Access Journal. Data transfer speed between hosts and the primary
array goes through two phases. In one phase, the data transfer speed remains almost unchanged.
In the other phase, the data transfer speed temporarily increases.
Figure 13 Data transfer speed of journal volumes
As illustrated in Figure 13 (page 54) , the data transfer speed (that is, the speed for reading and
writing) of journal volumes in the master journal group must exceed the amount of temporary
increase in data to be transferred. If the journal volumes' data transfer speed is below the amount
of temporary increase in data to be transferred, journal data for the temporary increase in data
to be transferred is not stored in journal volumes in a timely manner.
In Figure 13 (page 54) , the data transfer speed between the primary and the secondary arrays
indicates the transfer speed of journal data between the primary and secondary arrays. For more
information, see
Journal volumes in restore journal groups .
RAID group and journal group configurations
A RAID group can consist of physical volumes with a different number of revolutions, physical
volumes with different capacities, and physical volumes with different RAID configurations (for
example, RAID-1 and RAID-5). A RAID group's data transfer speed is affected by the physical
volumes and RAID configurations.
54 XP Continuous Access Journal operations requirements and restrictions