HP XP P9500 Storage - Manual (Page 127)

Mirror IDs are assigned to each pair. You assign arbitrary numbers as mirror IDs. For example:
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Local site mirror ID: M)
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Intermediate site secondary mirror ID: M; primary mirror ID: N)
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Remote site secondary mirror ID: N
Related information
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“Failure recovery” (page 127)
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“Requirements, restrictions, and notes” (page 127)
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“Problems that can occur with delta resync” (page 128)
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“Setting up the 3 Cnt Ac-J DC cascade configuration” (page 128)
Failure recovery
In a 3DC cascading configuration with three Cnt Ac-J sites, failure recovery utilizes the pair or
volume whose status is normal.
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If a failure occurs at the local site, business operations are moved to the intermediate site.
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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.
See “Recovery for 3 Cnt Ac-J DC cascade configuration” (page 93) for recovery information and
procedures.
Requirements, restrictions, and notes
•
Remote command devices must be assigned to two mirror IDs: one for the primary-intermediate
pair, and one for the intermediate-remote pair.
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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.
Alternatively, if microprogram version 70-03-xx or higher is installed, you can use RAID
Manager to register the mirrors in the journal. Contact HP support to ensure that you have the
latest firmware version available.
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Perform one pair operation in a 3 Cnt Ac-J 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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LUSE volumes cannot be used as pair volumes.
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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, for example, 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.
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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 COPY status in its role
as the primary-to-intermediate S-VOL, or the pair will not be created.
3 Cnt Ac-J DC cascade configuration 127