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

Note: If a path is definedfromahost to avolume, youcannotregisterthe volume as a journal
volume.
You can use the Remote Web Console computers to register journal volumes.
If
you ad d a journal volume when a remote copy operation is in progress (that is, when at
least one data volume pair exists for data copying), the metadata area of the journal volume
(see “Journal Volume Areas” on page 26) will be unused and only the journal data area will be
used. To make the metadata area usable, you need to split (suspend) all the data volume pairs in
the
journal group and then restore (resynchronize) the pairs.
Adding journal volumes during a remote copy operation will not decrease the metadata usage
rate if the metadata usage rate is high.
Adding journal volumes during a remote copy operation may not change the journal data usage
rate until the journal volumes are used. To check the journal data usage rate, use the Usage
Monitor window (see “Usage Monitor Operations” on page 141).
• Deleting journal volumes:
You can delete journal volumes under any of the following conditions:
• When the journal group does not contain data volumes (that is, before you create a data
volume pair for the first time in the journal group, or after all data volume pairs are released)
• When all data volume pairs in the journal group are suspended.
You can use the Remote Web Console computers to delete journal volumes.
• Access from hosts to journal volumes:
If a path
is defined from a host to a volume, you cannot register the volume as a journal volume.
You cannot define paths from hosts to journal volumes. This means that hosts cannot read from
and write to journal volumes.
Journal Volume Areas
The journal volume consists of the m etadata area and the journal data area. The ratio of metadata area
to
journal d
ata area is common in the journal volumes within the journal group.
In the metad
ata
area, the metadata that manag es the journal data is stored. For further information on
the
metadata area, see Table 3 on page 30. The journal data that the metadata manages is stored in
the
journal data area.
Note: If th
e
metadata or the journal data cannot be stored for a given length of time because
the
metada
ta or journal da ta areas have become full with metadata or journal data that had not
been discarded, the pair is suspended due to a failure. Users can use the Remote Web Console
computer to specify this timeout period (Data overflow watch) as a journal group option. This tim eo ut
period must be within the range of 0 to 600 seconds. For d etails on journal group options, see
“Changing O p tions for a Journal Group” on page 119.
Host Failover Software
Host failover software, which transfers information between host ser vers at the primary and remote sites,
is a
critical component of any disaster recovery effort. Host failover is configured using the desired host
failover software product for the platform (for example, Microsoft Cluster Server) , depending on your
installation requirements and standards. The storage system RemoteWeb Consolesoftwareproductsdo
not
provide any host failover functions.
When Continuous Access Journal is used as a data migration tool, host failover is recommended, but not
required. When Continuous Access Journal is used as a disaster recovery tool, host failover is required to
ensure effective disaster recovery operations. When a Continuous Access Journal pair is suspended due
to an
error condition, the primary storage system generates sense information which should be transferred
to the
remote site via the host failover software for effective d isaster detection and recovery.
Continuous Access Journal Remote Copy Operations
Figure 5 on page 27 illustrates the two types of Continuous Access Journal remote copy o perations:
init
ial copy and up date c opy.
26
About
Continuous Access Journal Operations