HP StorageWorks XP Remote Web Console Software - Manual (Page 51)

Continuous Access XP Journal user guide 51
The total capacity of the 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 failure recovery measure is to reverse the primary and secondary
data volumes (that is, change the copy direction). To reverse the primary and secondary data volumes, you
must usually ensure that the data transfer speed is the same before and after you reverse the data volumes.
Therefore, when you plan for master journal volumes and restore journal volumes, you must apply the same
scheme to the master and restore journal volumes.
If you do not want to reverse the primary and secondary data volumes, you can cope with a temporary
increase in data transfers and a communications path failure between the primary and secondary disk
arrays if the master journal volume satisfies the conditions mentioned earlier. Therefore, the data transfer
speed and volume capacity required for restore journal volumes are smaller than those required for master
journal volumes. The data transfer speed for journal volumes must exceed the data transfer speed in
“normal status.”
Factors that determine the data transfer speed between the primary and secondary disk arrays
The speed of data transfer between the primary and secondary disk arrays depends on the following
factors:
• Bandwidth of the data transfer paths
• DKC’s journal transfer speed
The data transfer speed between the primary and secondary disk arrays must exceed the data transfer
speed in “normal status” shown in Figure 13 . If a temporary increase in transferred data occurs and the
data transfer speed between the primary and secondary disk arrays is exceeded, excess data is stored
temporarily in journal volumes.
Figure 13 Data transfer speed between primary and secondary disk arrays
Bandwidth of data transfer paths
The bandwidth (that is, the data transfer speed) of data transfer paths between the primary and secondary
disk arrays depends on your environment. The bandwidth must exceed the data transfer speed in “normal
status” mentioned previously.
Journal transfer speed of DKCs
The journal transfer speed of a DKC depends on the number of paths used for transferring journals. The
number of paths for transferring journals must be large enough that the journal transfer speed exceeds the
data transfer speed in the “normal status” mentioned previously. The maximum number of paths for each
pair of the primary and secondary DKC is 8.