HP StorageWorks XP Remote Web Console Software - Manual (Page 52)

Journal Volume Capacity
In Figure 13 (page 52) , the size of the shaded area indicates the amount of journal data to be
stored in journal volumes as a result of temporary increase in data transferred.
If a temporary communication path failure occurs between the primary storage system and the
secondary storage system, journal transfers between the primary storage system and the secondary
storage system will stop temporarily. If hosts transfer data to the primary storage system while
journal transfers between the primary storage system and the secondary storage system are stopped
temporarily, all the data transferred from hosts to the primary storage system will be stored as
journal data in journal volumes.
Figure 13 Data Transfer Speed with URz (Influence on Journal Volume Capacity)
The following factors determine the required journal volume capacity:
•
the period of time during which data transfer can continue between hosts and the primary
storage system when a temporary increase in transferred data occurs or when a communication
path failure occurs between the primary and secondary storage system.
•
the data transfer speed for the period of time that is mentioned above
To determine the journal volume capacity, use the following formula. In this formula, VH-M is the
data transfer speed between hosts and the primary storage system. VM-R is the data transfer speed
between the primary storage system and the secondary storage system. t is the length of time during
which data transfer can continue.
Journal volume capacity > VH-M - VM-R × t
To calculate journal volume capacity that is required when a communication path failure occurs
between the primary storage system and the secondary storage system, assign 0 (zero) to VM-R.
The total capacity of journal volumes in each journal group must exceed the value illustrated above.
Journal Volumes in Restore Journal Groups
When a failure occurs at a host, one of the failure recovery measures is to reverse the primary
data volume and the secondary data volume (that is, change the copy direction). To reverse the
primary data volume and the secondary data volume, usually you must ensure that the data transfer
speed is the same before and after you reverse these data volumes. Therefore, when you do
planning on master journal volumes and restore journal volumes, you need to apply the same
scheme to both master and restore journal volumes.
52 Requirements and Restrictions for Universal Replicator z/OS Operations