HP StorageWorks XP Remote Web Console Software - Manual (Page 53)

Continuous Access XP Journal user guide 53
Planning for journal volumes
The data transfer speed for journal groups is affected by the journal volume specifications the journal
groups use. Therefore, to achieve the desired data transfer speed, you must consider these journal volume
specifications.
Considerations
This section explains what you need to consider when deciding on journal volume specifications.
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 11 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 Continuous Access XP
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 11 Data transfer speed of journal volumes
As illustrated in Figure 11 , 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 11 , 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 ” on page 55.