HP XP Continuous Access Software User Manual
Page 24
1.
The secondary array provides a status indicator number as management information to
distinguish (by sequence number), those data entries that have successfully been received at
the remote site. If the status is 1, that journal data has arrived at the secondary array. If the
status is 0, journal data has not arrived yet. The secondary array determines whether or not
journal data still needs to be settled according to this status indicator number. If journal data
has not arrived yet, the secondary array waits for the journal data.
2.
When the journal group's top queue indicates journal data has arrived, the secondary array
selects the journal data that has the lowest sequence number, and settles (de-stages) that
journal data.
3.
The secondary array repeats step 1 and step 2 to select and settle journal data.
illustrates journal data selection and settling at the secondary array. This
diagram shows that journal data S1 arrived at the secondary array because the management
information indicates 1. The secondary array selects journal data S1 to be settled, because S1 is
the lowest sequence number. When S1 is removed from the sequence number queue, journal data
S2 becomes the top entry, but it has not arrived yet. Journal data S2's management information
is 0. The secondary array waits for journal data S2. When journal data S2 arrives, the secondary
array selects S2 as the next journal data to be settled. The journal data that the secondary disk
selects is marked as “host-dirty” and treated as formal data.
Figure 6 Selecting and settling journal at the secondary array
The secondary array settles and restores journal data to the secondary data volume as follows:
•
Journal data stored in cache
Journal data is copied to the corresponding cached track and promoted to formal data.
•
Journal data stored in the restore journal volume
Journal data is read from the restore journal volume to cache. Journal data that is read to
cache is copied to the existing cache track and promoted to formal data. After that, the space
for the restore journal volume is released.
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Overview of XP Continuous Access Journal