HP XP P9500 Storage - Manual (Page 136)

Failure recovery
In a 3DC cascading configuration with three Cnt Ac-J Z sites, failure recovery utilizes the pair or
volume whose status is normal.
•
If a failure occurs at the local site, business operations are moved to the intermediate site.
•
If a failure occurs at the primary and intermediate sites, business operations are moved to the
remote site.
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When failed sites are restored, data is copied to their pair volumes from the current production
site, business operations are returned to the local site, and all pairs are restored.
Requirements, restrictions, and notes
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The P9500 system at the three sites require registration of two mirrors in one journal (since
two pairs use the same volume). This is done using the Edit Journal Volumes dialog box in
Remote Web Console, and is discussed in the setup procedure.
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Perform one pair operation in a 3 Cnt Ac-J Z DC configuration at a time. Performing pair
operations on the two pairs at the same time results in failure. If this occurs, correct the pair
statuses then perform the operations one-at-a-time.
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To share a Cnt Ac-J Z pair volume on the local site with a Compatible FlashCopy target volume
(T-VOL), set the mirror status for the Cnt Ac-J Z intermediate-remote pair to SUSPEND.
Also, when attempting this configuration, the local-intermediate pair will be suspended with
an error if both of the following are true:
◦ The mirror status for the local-intermediate pair is PAIR
◦ The mirror status for the intermediate-remote pair is COPY
•
Create the local-intermediate pair first; then create the intermediate-remote pair.
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Make sure that performance for the intermediate-remote data path is the same as performance
for the local-intermediate data path. Otherwise, the intermediate site’s journal volume may
experience increased usage. If the usage rate reaches the threshold, the pair
intermediate-remote pair is suspended.
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To maintain consistency among the pairs in related journals, make sure that all data volumes
in the journals are used in pairs (with accompanying registered mirrors). If a data volume in
the local site journal, is not used in a pair, the number of data volumes in the journal may not
be the same as the number in the secondary journal, and so consistency cannot be maintained.
•
When creating the local-intermediate pair, set the mirror status for the intermediate-remote
pair to Initial or Stopped.
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When creating the intermediate-remote pair, the P-VOL cannot be in Pending status in its role
as the primary-to-intermediate S-VOL, or the pair will not be created.
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When splitting the intermediate-remote pair using flush mode, set the pair’s mirror status to
Stopped.
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When restoring the local-intermediate pair, the intermediate-remote pair is split automatically
if its mirror status is PAIR.
•
The local-intermediate pair cannot be restored when the mirror status for the intermediate-remote
pair is COPY.
•
When deleting the intermediate-remote pair:
If Mirror is specified for Range, set the mirror status for either cascade pair to Stopped. ◦
◦ If Volume is specified for Range, set the mirror status for the primary-intermediate pair to
Stopped, or set pair status to SUSPEND.
136 3 Cnt Ac-J Z data-center configurations