HP XP7 Storage - Manual (Page 165)

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.
Table 37 (page 165) 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 37 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
Continuous Access Synchronous, Business Copy, and Continuous Access Journal operations 165