HP StorageWorks XP Remote Web Console Software - Manual (Page 68)

Data transfer
speed
Data transfer speed
between hosts and
the MCU
Data transfer speed of journal volumes
Data transfer speed
between the MCU and the RCU
Normal status Temporary increase in
data to be transferred
Time
Figure 13 Data Transfer Speed with URz (Data Transfer Speed of Journal Volumes)
As illustrated in Figure 13 on page 68, the data transfer speed (i.e., 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 timely.
In
Figure 13 on page 68, data transfer speed between the primary storage system and the secondary
storage system indicates transfer speed of journal data between the primary storage system and the
secondary storage system.
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 (e.g., RAID-1 and RAID-5). Data
transfer speed of RAID groups is affected by physical volumes and 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. 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 drop in the
data transfer speed of journal volumes. To avoid 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 (i.e., 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 indicates the data transfer speed of journal volumes mentioned earlier in
Data Transfer Speeds for Journal Volumes on page 67.
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 (i.e., the speed for writing and reading)
required for journal volumes, determine physical volume configuration and RAID configuration of RAID
groups, and create journal volumes in the RAID groups.
68 Preparing for Universal Replicator z/OS Operations