HP XP P9500 Storage - Manual (Page 30)

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In a bidirectional configuration, if all data paths for the primary system of the reverse direction
pair are disconnected when-pair status is changing to PSUE, the disconnection may not be
detected.
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If all the data paths for Continuous Access Synchronous pairs are disconnected, but the paths
used for Cnt Ac-J pairs are connected, failure suspend does not occur and S-VOLs cannot be
changed to PSUE status.
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If turning off the power of the primary system when S-VOLs are in PAIR status, all the data
paths for the primary system will be disconnected and all the S-VOLs registered in the CTG
No. 127 will be changed to PSUE status.
Other split/suspend behavior with consistency groups
The following applies to system behavior with consistency groups in general (no special conditions
as above):
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Pairsplit or system suspend operations are not executed until after data transfer is completed.
This applies when I/O processing is unfinished on a pair or multiple pairs that have been
either split the user or suspended because of system failure. The data transfer completes, then
the split or suspend operation is executed.
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However, if a split or suspend operation on the group is in progress when I/O processing on
a pair or pairs begins, the split operation on the pair or pairs is given priority. After the pair
has been split, I/O is accepted.
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Data consistency cannot be insured under certain circumstances. For example:
A port is blocked ◦
◦ A split command is in progress
◦ I/O processing begins
In this case, the resync command must be executed on the group and then the split can be
performed.
Host failover software
Host failover software transfers information between host servers at the local and remote sites. It
is a critical component of a disaster recovery solution.
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When Continuous Access Synchronous is used as a disaster recovery tool, host failover is
required to insure effective recovery operations.
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When Continuous Access Synchronous is used as a data migration tool, host failover is
recommended.
Continuous Access Synchronous does not provide host-failover functions. Use the failover software
most suitable for your platform and requirements (for example, Microsoft Cluster Server).
30 Planning for Continuous Access Synchronous