HP XP Continuous Access Software User Manual
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the contingency DC2-to-DC3 XP Continuous Access Journal pair for the delta resync operation in
becomes synchronized and usable.
When performing a DC2-to-DC3 delta resync operation, first the journal data in DC2 primary
site B is copied to the XP Continuous Access Journal secondary site via a journal copy. In this
journal copy operation, only journal data that is not yet sent to the secondary data volume in the
DC3 XP Continuous Access Journal secondary site is copied in chronological order. When the
journal copy operation completes, the journal restore operation takes place in the DC3 XP
Continuous Access Journal secondary site.
In a DC2-to-DC3 delta resync operation, the XP Continuous Access Journal pair's status does not
change to COPY, but changes to PAIR. This is because the delta resync operation copies only the
necessary data using the journal copy operation. Compared to the usual way that copies all the
data in the primary data volume, the delta resync operation requires much less time for recovering
the XP Continuous Access Journal pair after a failure occurs.
When the stored journal data's total capacity exceeds 80% of the journal volume of the XP
Continuous Access Synchronous secondary site, old journal data is automatically deleted. Therefore,
if the total capacity of journal data that is not restored to the XP Continuous Access Journal secondary
data volume exceeds 80% of the journal volume, the secondary data volume cannot be completely
restored by copying the journal data to the restore journal volume in the XP Continuous Access
Journal secondary site. In that case, according to the setting of the journal group option, all data
in the primary data volume is copied to the secondary data volume, or the delta resync operation
finishes without any further processing. In other words, any contingency to avoid a full DC2-to-DC3
copy in the event of a DC1 problem will be abandoned if the difference between the DC2 and
DC3 data get too large to store all the necessary delta data.
Usually, if the pair between the XP Continuous Access Synchronous primary and secondary sites
is synchronized periodically, the total capacity of journal data that is not restored to the XP
Continuous Access Journal secondary site does not exceed 80% of the journal volume. Although,
for example, if the XP Continuous Access Journal pair is suspended and the pair has not been
resynchronized for a long time, journal data of more than 80% of the journal volume capacity
might exist before it is restored to the XP Continuous Access Journal secondary data volume. In
such cases, you cannot perform the delta resync operation.
CAUTION:
Even if the journal data's capacity does not exceed 80% of the journal volume, journal
data is or might be destroyed in the following cases:
•
When restoring the XP Continuous Access Synchronous pair, then updating the P-VOL
•
When restoring the XP Continuous Access Journal pair between the primary site and the XP
Continuous Access Journal secondary site, then updating the P-VOL
•
When retry processing occurs because of a delay in a P-VOL update
•
When update processing for the XP Continuous Access Synchronous S-VOL is delayed
As shown in
, after the delta resync operation is performed completely and
primary site A (DC1) is recovered from its failure, the XP Continuous Access Journal pair between
primary site A (DC1) and the original XP Continuous Access Journal secondary site (DC3) is then
a candidate for a contingency delta resync pairing to prepare for the eventuality of a failure at
primary site B (DC2). For more information about requirements regarding a delta resync operation,
see
Requirements for performing delta resync operations
XP Continuous Access Journal data volume pair status
XP Continuous Access Journal displays the pair status for each data volume of a specified CU
Image (CUI) in the connected local array.
describes the XP Continuous Access
Journal data volume pair statuses. The primary array maintains the primary data volume's status
and can change the pair status of the primary and secondary data volumes. The secondary array
maintains the secondary data volume's status and can change the pair status of the secondary
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Overview of XP Continuous Access Journal