Hitachi ShadowImage for z/OS user guide (HIT9503-96007, October 2007)

ShadowImage for z/OS user guide 107
Figure 52 Ex. Consist. Group w/FlashCopy(R) Mirror Ver. 2: Copying Mult. Data Stored over Mult. Vols.
Figure 51 illustrates the example of copying the data stored over the volumes #1-#3 to the volumes #4-#6.
You need to create pairs of volume #1 and #4, #2 and #5, and #3 and #6, then copy the data. However,
if the volume #1 is updated before the creation of the Pair B (pair of #2 and #5) completes, the
consistency of the data in the copy target cannot be maintained.
In, Figure 52, Data 2 in the volume #2 references Data 1 in the volume #1, and Data 3 in the volume #3
references Data 2 in the volume #2. Therefore, when you try to copy Data 1-3 to the volume #4-#6, if Data
1 is updated before the copying processing of Data 2 completes, consistency of copied Data 1 and
copied Data 2 cannot be maintained.
To prevent the abovementioned problems, FlashCopy Mirror Version 2 regards volumes #1-#3 as one
consistency group, and allows you to suspend the write operation from the host to the FlashCopy Mirror
Version 2 S-VOLs until the Pair A, Pair B, Pair C are all created and all the copying processing is finished.
To suspend the write operation from the host to FlashCopy Mirror Version 2 S-VOLs by using consistency
groups, you need to issue the pair creation command with an option parameter. For information about the
pair creation command and the option parameter, see ”TSO Command Supported by Compatible
Mirroring for IBM FlashCopy Version 2” on page 132. For the information about the example of using the
command, see ”Creating FlashCopy Mirror Version 2 Pairs: FCESTABL” on page 135.
NOTE: When FlashCopy® Mirror Version 2 and TCz share volumes, the results of operations such as
creating pairs will differ according to whether you are using a consistency group or not. For details,
”Combining Compatible Mirroring for IBM® FlashCopy® Version 2 With ShadowImage for z/OS®” on
page 117.
Incremental FlashCopy Function
The Incremental FlashCopy allows you to maintain a relationship even after the copy operation from the
copy source to the copy target is completed. Also, when the S-VOL or the T-VOL is updated during or after
the copy operation, the updated part will be managed in a track as differential data. If you re-execute the
command to establish a relationship on the relationship established by the Incremental FlashCopy function,
only the differential data will be copied. The following figure shows the workflow from the establishing of