HP StorageWorks XP Remote Web Console Software - Manual (Page 100)

primary storage system goes through two phases; in one phase the data transfer speed remains
almost unchanged, and in another phase the data transfer speed increases temporarily.
Figure 42 Data Transfer Speed with Universal Replicator for Mainframe (Data Transfer Speed of
Journal Volumes)
As illustrated in Figure 42 (page 100) , 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 the journal volumes timely.
In Figure 42 (page 100) , the data transfer speed between the primary storage system and the
secondary storage system indicates the transfer speed of journal data between the primary storage
system and the secondary storage system.
Planning the RAID Group Configuration and Journal Group Configuration
A RAID group can consist of physical volumes with different numbers of revolutions, physical
volumes with different capacities, and physical volumes with different RAID configurations (for
example, RAID-1 and RAID-5). The data transfer speed of RAID groups is affected by the physical
volumes and the RAID configurations.
The data transfer speed of a journal volume depends on the data transfer speed of the RAID group
that the journal volume belongs to. One RAID group can consist of one or more volumes, including
journal volumes. Therefore, if frequent accesses are made to non-journal volumes in a RAID group,
relatively fewer accesses can be made to journal volumes in the same RAID group, and this can
cause a drop in the data transfer speed of journal volumes. To avoid a drop in the data transfer
speed of journal volumes, you will need to consider, for example, relocating the journal volumes
and the frequently accessed non-journal volumes (that is, placing the journal groups in one RAID
group and placing the frequently accessed non-journal volumes in another RAID group).
Arranging Journal Volumes
The following formula indicates the data transfer speed of journal volumes mentioned earlier in
“Computing the Required Data Transfer Speeds for Journal Volumes” (page 99) .
If a host attempts to write data of aa kilobytes and the number of write I/Os per second is bb, the
data transfer speed required for journal volumes is calculated as follows:
Data transfer speed of journal volumes > aa × bb ÷ 1,024 (MB/sec)
The data transfer speed of journal volumes must exceed the data transfer speed from hosts to the
primary storage system. You must consider the data transfer speed (that is, the speed for writing
and reading) required for journal volumes, determine the physical volume configuration and RAID
configuration of the RAID groups, and create journal volumes in the RAID groups.
100 Preparing for Universal Replicator for Mainframe Operations