HP StorageWorks XP Remote Web Console Software - Manual (Page 110)

of temporary increase in the data to be transferred, the journal data for the temporary increase in
the data to be transferred will not be stored in journal volumes in a timely manner.
In Figure 50 (page 109) , 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 secondary storage system. For details, see
“Journal Volumes in Restore
Journal Groups” (page 111) .
RAID Group Configuration and Journal Group Configuration
A RAID group can consist of physical volumes with rotational speeds, physical volumes with different
capacities, and physical volumes with different RAID configurations (for example, RAID1 and
RAID5). The data transfer speed of RAID groups is affected by the physical volumes and RAID
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 accesses 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 data 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 groups in one RAID
group and placing the frequently accessed non-journal volumes in another RAID group).
Arranging Journal Volumes
The following formula indicates the data transfer speed of the journal volumes mentioned earlier
in
“Data Transfer Speed Required for Journal Volumes” (page 109) .
If a host attempts to write data of aa kilobytes and the number of write I/Os per second is bb, the
data transfer 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 primary storage system. You must consider the data transfer speed (that is, the speed for writing
and reading) required for the journal volumes, determine the physical volume configuration and
RAID configuration of the RAID groups, and create the journal volumes in the RAID groups.
Journal Volume Capacity
In Figure 51 (page 111) , the size of the shaded area indicates the amount of journal data to be
stored in the journal volumes as a result of a temporary increase in the data transferred.
If a temporary communications 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 the 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 the hosts to the primary storage system will be stored as
journal data in the journal volumes.
110 Preparing for XP Continuous Access Journal Operations