Data transfer speed 
Data transfer speed of journal volumes
Data transfer speed
between the MCU and the RCU
Data transfer speed between hosts and the MCU
Time
Normal status | Temporary increase in |
| data to be transferred |
Figure 3-31 Data Transfer Speed with URz (Data Transfer Speed of Journal Volumes)
As illustrated in Figure 3-31, 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 3-31, 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.
Planning 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.
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Hitachi Universal Replicator for IBM /OS User’s Guide
