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

Primar
y
site
Secondar
y
site
Primar
y
host
Secondar
y
host
Write instruction
Primar
y
stora
g
e s
y
stem Secondary storage system
Primary
data
volume
Issuing Read
Journal command
Journal restore
function
Journal obtain
function
Journal co
py
function
Secondary
data
volume
Master
j
ournal
volume
Restore
j
ournal
volume
Figure 1 C ontinuous Access Journal Com ponents for a Fibre C h annel Connection
Journal Obtain
Journal obtain is the function to store the already stored data in the primary data volume as a base-journal
in the
journal volume at the primary site. And then this function stores the write data as a journal data in
the
journal volume with every update of the primary data volume according to the write instruction from
the
host. The journal obtain operation is performed according to the instruction for the pair create or
pair resync operation from the primary site. The write sequence number from the host is assigned to
the
journal data. According to this information, the write sequence consistency at the secondar y site
canbemaintained. The update data from thehostiskeptinthe cache. Therefore, thejournal obtain
function for the update data is performed at a time other than the receipt of update data from the
host or the storage of data to the data volume.
Journ
al
Copy
Journal copy is the function to copy the data in the master journal volume at the primary site to the restore
journ
al
volume at the secondary site. The secondary storage system issues the read journal command
to the
primary storage system to request the transfer of data tha t is stored in the ma ster journal volume
acco
rding to the pair create or pair resync operation instruction from the primary site. The primary
stor
age
system transfers the data in the journal volume to the secondar y site according to the read journal
comm
and, if it has journal data that should be sent. If the primary storage system does not have journal
dat
a, the information is sent. The secondary storage system stores the journal volume data that is sent
fro
m
the primary site in the restore journal volume at the secondar y site. The read journal commands are
issued repeatedly and regularly from the secondary site to the primary site until the journal operation is
stopped. After the data is restored, the journal sequence numbers are sent from the secondar y site to
the primary site when the read journal command is issued. According to this information, the journal
da
ta at the primary site is discarded.
Journal Restore
Journal restore is the function to reflect the stored data in the restore journal volume to the secondary data
volume at the seconda ry site. The data in the restore journal volume is restored to the secondary data
volume according to the write sequence number. This will ensure write sequence consistency between the
primary and secondary data volumes. After the journal data is restored to the secondary data volume,
the
journal data is discarded at the secondary site.
18
About
Continuous Access Journal Operations