HP XP P9500 Storage User Manual
Page 151
Figure 54 Continuous Access Asynchronous suspension condition
Continuous Access Synchronous/Continuous Access Asynchronous and Continuous
Access Journal fence level settings
Continuous Access Synchronous volume pairs are assigned a fence level for write I/Os to ensure
mirroring consistency of critical volumes. When the secondary volume takes over from the primary
volume, the takeover action is determined according to the pair status and fence level of the
corresponding secondary volume.
shows the relationship between Continuous
Access Synchronous pair statuses and fence levels.
•
Mirror consistency = Identity and sequence of data is assured via error notification after an
I/O completion.
•
Data consistency = Sequence of data is assured in I/O order based on host.
Table 35 Relationship between Continuous Access Synchronous pair statuses and fence levels
Fence level and write response
Continuous Access Synchronous pair status of
volume
Async [4]
Never [3]
Status [2]
Data [1]
OK
OK
OK
OK
Data consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
assured
OK
OK
OK
ERROR
Data consistency
assured
Mirroring
consistency not
assured
Mirroring
consistency not
assured
Mirroring
consistency
assured
OK
OK
ERROR
ERROR
Data consistency
assured
Mirroring
consistency not
assured
Mirroring
consistency
assured
Mirroring
consistency
assured
[1] When the fence level is data: Mirroring consistency is assured, since a write error is returned if mirror consistency with the
remote S-VOL is lost. The secondary volume can continue operation, regardless of the status. Note: A P-VOL write that discovers
a link down situation will, in addition to returning an error to the host, likely be recorded on [only] the P-VOL side.
[2] When the fence level is status: If there is a mirror consistency problem (that is, PSUE) and it is possible to set the S-VOL to
PSUE, the P-VOL write completes OK. If the S-VOL cannot be set to PSUE for any reason, the P-VOL write completes with an error.
The mirror consistency of the S-VOL depends on its status:
Continuous Access Synchronous, Business Copy, and Continuous Access Journal operations
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