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Table 6-9 Relationship between TrueCopy pair statuses and fence levels
TrueCopy pair status of volume
Fence level and write response
Data [1]
Status [2]
Never [3]
Async [4]
OK
OK
OK
OK
Mirroring
consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
assured
Data
consistency
assured
ERROR
OK
OK
OK
Mirroring
consistency
assured
Mirroring
consistency
not assured
Mirroring
consistency
not assured
Data
consistency
assured
ERROR
ERROR
OK
OK
Mirroring
consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
not assured
Data
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:
PSUE: The secondary volume is dubious.
PAIR: The secondary volume can continue operation.
[3] When the fence level is never: Writing to the P-VOL is still enabled in the state where mirror
consistency to the S-VOL is lost, regardless of whether the secondary volume status is updated or not.
Thus, the secondary could have these states:
PSUE: The secondary volume is dubious.
PAIR: The secondary volume is substantially dubious, since it can continue operation and is also dubious.
The P-VOL status must be checked to confirm the mirroring consistency.
[4] When the fence level is async: TrueCopy Async/UR uses asynchronous transfers to ensure the
sequence of write data between the P-VOL and S-VOL. Writing to the P-VOL is enabled, regardless of
whether the S-VOL status is updated or not. Thus the mirror consistency of the secondary volume is
dubious (similar to the "Never" fence):
•
PSUE: The S-VOL mirroring consistency is not assured, but the PSUE suspended state ensures the
sequence of data for the consistency group; thus, data consistency is also assured during a PSUE
state. At a PSUE state, the P-VOL writes still complete and are also noted in a bitmap for future
Data replication operations with CCI
6-31
Command Control Interface User and Reference Guide
Summary of Contents for HUS VM
Page 10: ...x Command Control Interface User and Reference Guide ...
Page 18: ...xviii Preface Command Control Interface User and Reference Guide ...
Page 78: ...2 50 CCI software environment Command Control Interface User and Reference Guide ...
Page 154: ...4 8 Starting up CCI Command Control Interface User and Reference Guide ...
Page 191: ...Provisioning operations with CCI 5 37 Command Control Interface User and Reference Guide ...
Page 280: ...6 56 Data replication operations with CCI Command Control Interface User and Reference Guide ...
Page 286: ...6 62 Data replication operations with CCI Command Control Interface User and Reference Guide ...
Page 302: ...7 16 Data protection operations with CCI Command Control Interface User and Reference Guide ...
Page 324: ...8 22 Examples of using CCI commands Command Control Interface User and Reference Guide ...
Page 524: ...9 200 Troubleshooting Command Control Interface User and Reference Guide ...
Page 529: ...Command Control Interface User and Reference Guide ...