HP StorageWorks XP24000 Continuous Access Journal Software User and Reference Guide, v01 (T5278-96001, June 2007)

data volume and the secondary data volume, usually you must ensure that the data transfer speed is
the
same before and after you reverse the data volumes. Therefore, when you do planning on master
journal volumes and restore journal volumes, you need to apply the same scheme to both the master
and restore journal volumes.
If you do not want to reverse the primary da ta volume and the secondary data volume, you will be
able
to co pe with a temporary increase in d ata transfers and a communications path failure between
the
primary storage system and the secondary storage system if the m aster journal volume satisfies the
conditions mentioned earlier. Therefore, the data transfer speed and the volume capacity required for the
restore journal volumes are smaller than those required for the master journal volumes. Note that the data
transfer speed for the journal volumes must exceed the data transfer speed in normal status.
Factors that Determine the Data Transfer Speed between the
Primary Storage System and the Secondary Storage System
The speed of the data transfer between the primary storage system and the secondary storage system
depends on the following factors:
•
The bandwidth of the data transfer paths (see “Bandwidth of Data Transfer Paths”onpage73)
•
The journal transfer speed of the DKC (see “Journal Transfer Speed of the D KC” on page 74)
The data transfer speed between the primary storage system and the second ary storage system must
exceed the data transfer speed in normal status mentioned in Figure 34 on page 73. If a temporary
increase in transferred data occurs a nd the data transfer speed between the primary storage system and
the
secon
dary storage system is exceeded, the excess data will be stored temporarily in the journal
volumes.
Data transfer
Data transfer speed
between hosts and
the MCU
Data transfer speed of journal volumes
Data transfer speed
between the MCU and the RCU
Time
speed
Normal status
Temporary increase in
data to be transferred
Figure 34 Data Transfer Speed with Continuous Access Journal (Da t a Transfer Speed
between thePrimary StorageSystemand theSecondary StorageSystem)
Bandwidth of Data Transfer Paths
The bandwidth (that is, the data transfer speed) of the da ta transfer paths bet ween the primary storage
syst
em
and the secondary storage system depends o n the user's environment. The bandwidth must
exce
ed the data
transfer speed in normal status mentioned earlier.
XP24000 Continuous Access Journal Software User a nd Reference Guide
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