Hitachi TAGMASTORE MK-90RD011-25 - Manual (Page 47)

Hitachi Command Control Interface (CCI) User and Reference Guide 29
Table 2.7 Relationship between Hitachi TrueCopy Pair Status and Fence Level
Fence Level and Write Response
Hitachi TrueCopy Pair Status of Volume Data [1] Status [2] Never [3] Async [4]
OK OK OK OK
Valid
P
Secondary volume
Valid
P
Primary volume
Write response
Mirroring
consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
assured
Data
consistency
assured
ERROR OK OK OK
Not Valid
E
Secondary volume
Valid
E
Primary volume
Write response
Mirroring
consistency
assured
Mirroring
consistency
not assured
Mirroring
consistency
not assured
Data
consistency
assured
ERROR ERROR OK OK
Not Valid
P
Secondary volume
Valid
E
Primary volume
Write response
Mirroring
consistency
assured
Mirroring
consistency
assured
Mirroring
consistency
not assured
Data
consistency
assured
Mirror consistency = Identity of data and sequence of data are assured via error notification
as an I/O completion.
Data consistency = Sequence of data is assured in I/O order based on host.
[1] When fence level is data: Mirroring consistency is assured, since a write error is returned
if mirror consistency with the remote SVOL is lost. The secondary volume can continue
operation, regardless of the status. Note: A PVOL write that discovers a link down situation
will, in addition to returning an error to the host, likely be recorded on [only] the PVOL side.
[2] When fence level is status: If there is a mirror consistency problem (i.e., PSUE) and it is
possible to set the SVOL to PSUE, the PVOL write completes OK. If the SVOL cannot be set to
PSUE for any reason, the PVOL write completes with an error. The mirror consistency of the
SVOL depends on its status:
„
PSUE: The secondary volume is dubious.
„
PAIR: The secondary volume can continue operation.
[3] When fence level is never: Writing to the PVOL is still enabled in the state where mirror
consistency to the SVOL 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.