IBM System storage DS6000 Series, Redbook

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Chapter 9. FlashCopy interfaces
99
Group has been formed. During the time period between the first and last volumes being
frozen, no dependent write updates will occur, which allows a consistent copy of logically
related data that spans multiple volumes.
Freezing the source volumes: You can use the FCCGFREEZE keyword on the COPY
FULL or COPY TRACKS CPVOLUME command to specify that the FlashCopy source
volume is to be part of a FlashCopy Consistency Group. Subsequent I/O activity to the
source volumes will be held (frozen) as each volume is copied. A frozen volume remains
in long busy state until the Consistency Group Created (
thaw
) command is processed on
the logical subsystem (LSS) where the volume resides, or when the FlashCopy
Consistency Group timer expires.
Thawing the frozen volumes: When all volume copy operations have completed, you can
use the DFSMSdss CGCREATE command to allow I/O activity to resume on the frozen
volumes (thaw the volumes) residing in the logical subsystems. The required
ACCESSVOL keyword specifies one or more volumes residing in the LSS to which the
thaw
command will be directed. Only one volume needs to be specified for each LSS
containing frozen volumes in the FlashCopy Consistency Group.
Verifying the Consistency Group: You can use the FCCGVERIFY keyword on the
CGCREATE command to validate the state of the FlashCopy Consistency Group before
thawing all the volumes. This will help you determine whether the copies of the group of
volumes are consistent. An error message is issued if the frozen state cannot be verified.
Regardless of the verification result, DFSMSdss will proceed to thaw all the volumes in the
designated logical subsystems.
򐂰 Establish a target on existing Metro Mirror primary
When this option is selected, the FlashCopy target volume can be, or can become, a
primary volume for a Metro Mirror or Global Copy relationship. When FlashCopy is not
invoked by the DFSMSdss utility, then FCTOPPRCPrimary is ignored.
When FCTOPPRCPrimary is not specified, or if the capability is not supported by the
DS6000, a Metro Mirror or Global Copy primary volume is not eligible to become a
FlashCopy target volume.
򐂰 Permit FlashCopy to occur if target volume is online for host access
When setting up the relationship, it is checked whether the target volume is online or not.
See Table 9-10 for valid combinations of
offline
and
online
for volumes.
Table 9-10 Resulting actions from target being online or offline
Note: A Metro Mirror volume pair in full duplex state will go to a duplex pending state
when the FlashCopy relationship is established. When Metro Mirror completes the copy
operation, the volume pair returns to the full duplex state.
Status of target
volume in z/OS Permit FlashCopy to
occur if target
volume is online Resulting action
volume is online not selected FlashCopy definition is not possible.
volume is online selected FlashCopy definition is queued until target
volume goes offline
volume is offline selected or not
selected FlashCopy will be started immediately