HP StorageWorks XP24000/XP20000 Continuous Access Journal Software User Guide (T5278-96048, November 2011)

Planning of Journal Volumes
This section explains what you need to consider when deciding on journal volume specifications.
Data transfer speed for journal groups is affected by the specifications of journal volumes that the
journal groups use. Therefore, you need to think about specifications of journal volumes to be used
by journal volumes, in order to achieve the data transfer speed that you want.
The following factors affect the speed for writing to and reading from journal volumes, particularly
when a temporary communications path failure occurs between the primary storage system and
the secondary storage system, or when the amount of data transferred from hosts to the primary
storage system is increasing:
• RAID configuration of the RAID groups that will contain the journal volumes
• Types of physical volumes in the RAID groups that will contain the journal volumes
• Frequency of access to non-journal volumes in the RAID groups that will contain the journal
volumes
• Data transfer speed required for the non-journal volumes mentioned above
• Disk usage rate for the RAID groups
The following factor affects the time during which data transfer with hosts can continue without
being influenced by a temporary communications path failure between the primary storage system
and the secondary storage system or without being influenced by an increase in the data to be
transferred from the hosts to the primary storage system.
• Capacity of the journal volumes
Data Transfer Speed Required for Journal Volumes
Figure 50 (page 109) illustrates how the data transfer speed (that is, the amount of data to be
transferred per unit of time) will change as time elapses, citing different types of data transfer speed
with XP Continuous Access Journal. Data transfer speed between hosts and the primary storage
system goes through two phases: in one phase, the data transfer speed remains almost unchanged;
in the other phase, the data transfer speed increases temporarily.
Figure 50 Data Transfer Speed with XP Continuous Access Journal (Data Transfer Speed of Journal
Volumes)
As illustrated in Figure 50 (page 109), 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 data transfer speed of journal volumes is below the amount
Planning of Journal Volumes 109