Secondary data volume write option, Difference management, Journal processing – HP StorageWorks XP Remote Web Console Software User Manual
Page 28: Creating and storing journals at primary arrays, Table 3 metadata information, 3 metadata information, Secondary data, Volume write option, Table 3
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Overview of Continuous Access XP Journal
” on page 28). You can only enable the secondary data volume’s write option when
splitting the pair from the primary array.
NOTE:
To reduce the overhead associated with these remote copy activities and maximize data
transfers, the local array uses a special write command that is allowed only for Continuous Access XP
Journal initial and update copy operations. This command transfers control parameters and FBA-format
data for consecutive updated records in a track using a single write operation. The special Continuous
Access XP Journal write command eliminates the overhead required for performing FBA-to-CKD and
CKD-to-FBA conversions.
Secondary data volume write option
For additional flexibility, Continuous Access XP Journal provides a secondary data volume write option
(S-Vol. Write) that enables write I/Os to the secondary data volume of a split Continuous Access XP
Journal pair. You can select the secondary data volume’s write option during the pairsplit-r operation, and
it applies only to the selected pairs. You can access the secondary data volume’s write option only when
connected to the primary array. When you resync a split Continuous Access XP Journal pair that has the
secondary data volume’s write option enabled, the secondary array sends the secondary data volume
track bitmap to the primary array, and the primary array merges the primary and secondary data volume
bitmaps to determine which tracks are out-of sync. This ensures proper pair resynchronization.
Difference management
Changed track data (updated by write I/Os during split or suspension) between the primary and
secondary data volumes is stored in each track bitmap. When a split/suspended pair is resumed
(pvol-to-svol pairresync), the primary array merges the primary and secondary data volume bitmaps, and
uses that information to copy differential data to the secondary data volume.
NOTE:
The number of bitmap areas affects the maximum number of pairs you can create in the array.
For more information, see ”
Journal processing
Journal data contains primary data volume updates and metadata information (associated control
information), which enables the secondary array to maintain update consistency of the Continuous Access
XP Journal secondary data volumes.
Creating and storing journals at primary arrays
When a primary array performs an update (host-requested write I/O) on a Continuous Access XP Journal
primary data volume, the primary array creates journal data that is transferred to the secondary array.
Journal data is stored in cache first, and then in the journal volume.
Metadata information is attached to journal data (see
). When the base-journal is obtained, only
metadata information is created and stored in the Continuous Access XP Journal cache or journal volume.
Table 3
Metadata information
Type
Description
Journal type
Journal type (for example, base-journal or update journal)
LDEV No. (data)
Number of the primary data volume that stores the original data
Original data storing
position
Primary data volume’s slot number, and start and end of sub-block number (data
length)
LDEV No. (journal)
Volume number of the master journal volume that stores the journal data
Journal data storing position Master journal volume’s slot number, and start sub-block number