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

Data transfer
speed
Data transfer speed
between hosts and
the MCU
Data transfer speed of journal volumes
Data transfer speed
between the MCU and the RCU
Normal status
Temporary increase in
data to be transferred
Time
Figure 32 Data Transfer Speed with Continuous Access Journal (Data Transfer Speed
of
Journal Volumes )
As illustrated in Figure 32 on page 7 1, the data transfer speed (that is, the speed for reading and writing)
of journal volumes in the master journal g roup must exceed the am ount of temporary increase in the data
to be transferred. If the data transfer speed of journal volumes is below the a m ount of temporary increase
in
the dat
a
to be transferred, the journal data for the temporar y increase in the data to be transferred will
not be store d in journal volumes in a timely manner.
In Figure 32 on page 71, the data transfer speed between the primary storage system and the secondary
storage system indicates the transfer speed of the journal data between the primary storage system and
the seco
ndary storage system. For details, see “ Journal Volumes in Restore Journal Groups” on page 72.
RAID Group Configuration and Journal Group Configuration
A RAID group can consist of physical volumes with a different number of revolutions, physical volumes
with different capacities, and physical volumes with different RAID configu rations (for example, RAID-1
and
RAID-5). The data transfer speed of RAID groups is affected by the physical volumes and R A I D
configurations.
The data transfer speed of a journal volume depends on the data transfer speed of the RAID group to
which the journal volume belongs. One RAID group can consist of one or more volumes, including
journal volumes. Therefore, if frequent accesses are made to non-journal volumes in a RAID group,
relatively fewer a ccesses can be made to journal volumes in the same RAID group, and this can cause a
drop in the data transfer speed of the journal volumes. To avoid a drop in the da ta transfer speed of the
journal volumes, you will need to consider, for example, relocating the journal volumes and the frequently
accessed non-journal volumes (that is, placing the journal g roups in one RAID g roup and placing the
frequently accessed non-journal volumes in another R AID group).
Arranging Journal Volumes
The following indicates the data transfer speed of the journal volumes mentioned earlier in
“Data Transfer Speed Required for Journal Volumes” on page 70.
If a host attempts to write data of aa kilobytes and the number of write I/Os per second is bb, the data
tr
ansfer speed required for the journal volumes is calculated as follows:
Data transfer speed of journal volumes > aa × bb ÷1,024 (MB/sec)
The data transfer speed of the journal volumes must exceed the data transfer speed from hosts to the
pr
imary storage system. You must consider the data transfer speed (that is, the speed for writing and
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