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

Note: The number of bitmap areas affects the maximum possible number of pairs that can
be created in the storage system. For d etails on the maximum possible number of pairs, see
“Maximum Number of Pairs”onpage44.
Journal Processing
The Continuous Access Journal journal data contains the primary data volume updates and the metadata
information (
associated control information), which enables the secondar y storage system to maintain
update
consis
tency
of the Continuous Access Journal secondary data volumes. Continuous Access
Journal journal processing includes:
• Creating and storing journals at the primary storage system (see
“Journal P ro
cessing at the Primary Storage System” on page 30),
• Copying journals to the secondary storage system (see
“Journal Processing at the Secondary Storage System” on page 31),
• Storing jou
rnals at the secondar y storage system (see
“Storing Journals at the Secondary Storage System”onpage31),
• Selecting and restoring journals at the secondary storage system (see
“Selectin
g
and Restoring a Journal at the Secondary Storage System” on page 31) , and
•
Types of journals (see “Types of Journals” on page 31)
Journal Processing at the Primary Storage System
When a primary storage system per forms an update (host-requested write I/O) on a Continuous Access
Journal primary data volume, the primary storage system creates the journal data to be transferred
to the
secondary storage system. The journal data will be stored in the cache first, and then in the
journal volume.
Metadata information will be attached to the journal data (see Table 3 on page 30). When the
base-journal is obtained, only metadata information is created and stored in the Continuous Access
Journal cache or the journal volume.
Table 3 Metadata Information
Type
Description
Journal type Type of journal (for example, base-journal or update journal)
LDEV No. (data)
The number of the primary data volume that stores the original data
Original data storing position
The primary data volume slot number, and the start and end of the
sub-block number (data length)
LDEV No. (journal) The volume number of the master journal volume that stores the journal data
Journal data storing position
The slot number of the master journal volume, and the start sub-block
number
Journal sequence number The sequence number that is assigned when the journal is obtained
Timestamp
The time when the journal data is obtained
The journal sequence number indicates the primary data volume write sequence tha t the primary storage
system has created for each journal group. The journal data is transferred to the secondary storage system
asynchronously with the host I/O. The secondar y storage system updates the secondary data volume in
the
same o rder as the p rimary data volume according to the sequence number information in the journal.
Note: Continuous Access Journal processing continues uninterrupted if the SVP reboots or even if the
SVP fails.
30
About
Continuous Access Journal Operations