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

Journal Volumes
When Continuous
Access Journal is used, updates to primary data volumes can be stored in other
volumes, which are called journal volumes. The updates (which are sometimes referred to as update
data) that will be stored in journal volumes are called journal data.
Because journal
data
will be stored in journal volumes, you can perform and manage highly reliable
remote copy ope
rations without suspension of remote copy operations. For example:
Even if a communications path between the primary storage system and the secondary storage system
fails temporarily, remote copy operations can continue af ter the communications path is recovered.
If data transfer from hosts to the primary storage system is temporarily faster than data transfer between
the
primary st
orage system and the secondary storage system, remote copy o perations b etween the
primary storage system and the secondary storage system can continue. Because journal volumes can
contain a lot
more update data than the c ache memor y can contain, remote copy operations can
continue if
da
ta transfer from hosts to the p rimar y storage system is faster for a relatively long period of
time than dat
a
transfer between the p rimar y storage system and the secondar y storage system.
Number of Journal Volumes
One journal group can contain up to 64 journal volumes. Each of the journal volumes can have different
volume sizes and different RAID confi gurations. Journal data will be stored sequentially and separately
into each journal volume in the same journal group.
Specifications for Journal Volumes
• Types of log
ical units
(LUs):
The followi
ng
DKU emulation types are allowed for journal volumes:
Table 2 Emul
ation Types for Journa l Volum es
Emulation Category Suppor ted Emulation Types
OPEN-V
DKU (drive)
Note: You can only use OPEN-V volumes for journal volumes.
• Volumes and their capacity:
You can use V LL volumes for journal volumes.
Journal volumes in the same journal group can have different capacities. A master journal volume
and
the corresponding restore journal volume can have a different capacities.
A
journal volume consists of two areas: one area is used for storing journal data, and the other
area is used for storing metadata for remote copy.
• RAID configuration:
Journal volumes support all RA ID configurations that are supported by the storage system. Journal
volumes also support all physical volumes that are suppor ted by the storage system.
• Support for program products:
The volumes that are set using Cache Residency Man ager can be used for journal volumes.
Restrictions on Journal V olumes
• Registering journal volumes:
Caution: You must register journal volumes in a journal group before you create a data volume
pair
for the firsttimeinthe journalgroup.
You can add 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.
• When processing for changing the status of a data volume pair (for example, release or
suspension of a data volume pair) is not in progress
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