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

Figure 12 Data Transfer Speed with URz (Data Transfer Speed of Journal Volumes)
As illustrated in Figure 12 (page 51) , the data transfer speed (that is, the speed for reading and
writing) of journal volumes in the master journal group must exceed the amount of temporary
increase in data to be transferred. If the data transfer speed of journal volumes is below the amount
of temporary increase in data to be transferred, the journal data for the temporary increase in
data to be transferred will not be stored into journal volumes timely.
In Figure 12 (page 51) , data transfer speed between the primary storage system and the secondary
storage system indicates transfer speed of journal data between the primary storage system and
the secondary storage system. See
“Journal Volumes in Restore Journal Groups” (page 52)
RAID Group Configuration and Journal Group Configuration
A RAID group can consist of physical volumes of different number of revolutions, physical volumes
of different capacity, and physical volumes of different RAID configurations (for example, RAID-1
and RAID-5). Data transfer speed of RAID groups is affected by physical volumes and RAID
configurations.
The data transfer speed of a journal volume depends on the data transfer speed of the RAID group
that 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 drop in the data transfer speed of journal volumes. To avoid drop in the data transfer speed
of 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 indicates the data transfer speed of journal volumes mentioned earlier in “Data
Transfer Speeds for Journal Volumes” (page 50) .
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 journal volumes is calculated as follows:
Data transfer speed of journal volumes > aa × bb ÷ 1,024 (MB/sec)
The data transfer speed of 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 journal volumes, determine physical volume configuration and RAID
configuration of RAID groups, and create journal volumes in the RAID groups.
Planning of Journal Volumes 51