HP StorageWorks XP Remote Web Console Software - Manual (Page 101)

Computing the Journal Volume Capacity
In the following figure, the size of the shaded area indicates the amount of journal data to be
stored in journal volumes as a result of a 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 43 Data Transfer Speed with Universal Replicator for Mainframe (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, V
H-M
is the
data transfer speed between hosts and the primary storage system. V
M-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.
Formula 1: Journal volume capacity > V
H-M
- V
M-R
× t
To calculate the 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 V
M-R
.
The total capacity of the journal volumes in each journal group must exceed the value illustrated
in Formula 1 above.
When the data in the primary data volume of the Universal Replicator for Mainframe delta resync
pair is updated, if the journal data that exceeds the 70 percent of the journal volume capacity on
the primary site of the URz delta resync pair is generated, the delta resync operation will fail.
Therefore, adopt the larger value for the journal volume capacity on the primary site of the Universal
Replicator for Mainframe delta resync pair by comparing the value of the Formula 1 and Formula
2.
In Formula 2, V is the data transfer speed between a host and the primary storage system. t is the
length of time until the delta resync operation starts.
Formula 2: Journal volume capacity > (V x t ) x 1.5
Planning for Journal Volumes 101