HP StorageWorks XP Remote Web Console Software - Manual (Page 21)

and/or the pair is not suspended, the secondary storage system rejects all read and write I/Os to
a URz secondary data volume.
Difference Management
The differential data (updated by write I/Os during split or suspension) between the primary data
volume and the secondary data volume is stored in each track bitmap. When a split/suspended
pair is resumed (Resume Pair), the primary storage system merges the primary data volume and
secondary data volume bitmaps, and the differential data is copied to the secondary data volume.
The number of bitmap areas affects the maximum possible number of pairs that can be created in
the storage system. For details on the maximum possible number of pairs, see
The Maximum
Number of Pairs .
Journal Processing
The URz journal data contains the primary data volume updates and the metadata information
(associated control information), which enables the secondary storage system to maintain update
consistency of the URz secondary data volumes. URz journal processing includes:
•
Journal Processing at the Primary Storage System
•
“Copying Journals to the Secondary Storage System” (page 22)
•
Storing Journal at the Secondary Storage System
•
“Selecting and Restoring Journal at the Secondary Subsystem” (page 22)
•
“Types of Journals” (page 23)
Creating and Storing Journals at the Primary Storage System
When a primary storage system performs an update (host-requested write I/O) on a URz primary
data volume, the primary storage system creates a journal data to be transferred to secondary
storage system. The journal data will be stored into the cache at first, and then into the journal
volume.
Metadata information will be attached to journal data (see “Metadata Information” (page 21) ).
When base-journal is obtained, only metadata information is created and stored in UR cache or
the journal volume.
Table 3 Metadata Information
Description Type
Type of journal (for example, base-journal or update journal) Journal type
The number of primary data volume that stores the original data LDEV No. (data)
The primary data volume slot number, and the start and end of sub-block
number (data length) Original data storing position
The volume number of master journal volume that stores the journal data LDEV No. (journal)
The slot number of master journal volume, and the start sub-block number Journal data storing position
The sequence number that is assigned when the journal is obtained Journal sequence number
The time when the journal data is obtained Timestamp
The journal sequence number indicates the primary data volume write sequence that 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 secondary storage system updates the
secondary data volume in the same order as the primary data volume according to the sequence
number information in the journal.
Journal Processing 21