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56 IBM System Storage DS6000 Series: Copy Services with IBM System z
Figure 7-2 FlashCopy target is Metro Mirror (or Global Copy) primary
It is possible to create either the FlashCopy relationship first or the Metro Mirror (or Global
Copy) relationship first. However, in general it is better to create the FlashCopy relationship
first to avoid the initial sending of unnecessary data across to the Metro Mirror (or Global
Copy) secondary.
7.4 Incremental FlashCopy - refresh target volume
Incremental FlashCopy provides the capability to refresh a FlashCopy relationship, thus
refreshing the target volume.
In order for an Incremental FlashCopy to be performed, the FlashCopy relationship must first
be established with the
Start Change Recording and Persistent FlashCopy options enabled.
If Incremental
FlashCopy is invoked via the ANTRQST API or the TSO FCESTABL command
with the INCREMENTAL(YES) option, the FlashCopy target is write-inhibited. Any attempt to
write to the device during this period will be failed by the hardware and surfaced as an I/O
error, an error from the access method, or both.
With Incremental FlashCopy, the initial FlashCopy—
copy or nocopy—relationship between a
source and target volume is subject to the following (see Figure 7-3 on page 57):
FlashCopy with nocopy option
If the original FlashCopy was established with the
nocopy option, then the bitmap for the
target volume will be reset, and, of course, the updates on the target volumes are
overwritten. However, using the incremental option will automatically convert this
relationship to a copy relationship, and the background copy will begin.
Metro
Mirror
or
Global
Copy
primary
secondary
source
target
FlashCopy
Remote site
Local site
Metro
Mirror
or
Global
Copy
Attention: A refresh of the target volume will always overwrite any writes previously done
to the target volume.
Restriction: If a FlashCopy source has multiple targets, an incremental FlashCopy
relationship can be established with one and only one target.
Note: Incremental FlashCopy is supported at volume level, not for data set FlashCopy.