HP StorageWorks XP Remote Web Console Software - Manual (Page 49)

Continuous Access XP Journal user guide 49
Considerations
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 disk arrays or
when the amount of data transferred from hosts to the primary disk 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 capacity of the journal volumes 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
disk arrays or an increase in the data to be transferred from hosts to the primary disk 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 disk array 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 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 data transfer speed of journal volumes is below the amount of temporary increase in
data to be transferred, the journal data for the temporary increase in data to be transferred will not be
stored into journal volumes in a timely manner.
In
Figure 11 , the data transfer speed between the primary and the secondary disk arrays indicates the
transfer speed of journal data between the primary and secondary disk arrays. For more information, see
” Journal volumes in restore journal groups ” on page 51.
RAID group configuration and journal group configuration
A RAID group can consist of physical volumes of different number of revolutions, physical volumes of
different capacity, and physical volumes of different RAID configurations (for example, RAID-1 and
RAID-5). The data transfer speed of RAID groups is affected by the physical volumes and RAID
configurations.
The data transfer speed of a journal volume depends on the data transfer speed of the RAID group to
which the journal volume belongs. One RAID group can consist of one or more logical volumes, including
journal volumes. Therefore, if frequent accesses are made to non-journal volumes in a RAID group,