HP XP P9500 Storage - Manual (Page 12)

Figure 5 Using Consistency Groups with Compatible FlashCopy: Copying data stored over multiple
volumes
Figure 6 Using Consistency Groups with Compatible FlashCopy: Copying multiple data stored over
multiple volumes
The first figure shows copying the data stored over volumes #1-#3 to volumes #4-#6. You need to
establish relationships of volume #1 and #4, #2 and #5, and #3 and #6, then copy the data.
However, if volume #1 is updated before the creation of the Relationship B (pair of #2 and #5)
is completed, the consistency of the data in the copy target cannot be maintained.
The second figure shows Data 2 in volume #2 references Data 1 in volume #1, and Data 3 in
volume #3 references Data 2 in volume #2. Therefore, when you try to copy Data 1-3 to volume
#4-#6, if Data 1 is updated before the copying processing of Data 2 is completed, the consistency
of copied Data 1 and copied Data 2 cannot be maintained.
To prevent the problems indicated above, Compatible FlashCopy regards volumes #1-#3 as one
consistency group, and enables you to suspend the write operation from the host to the Compatible
FlashCopy S-VOLs until the Relationship A, Relationship B, and Relationship C are all created and
all the copying processing is finished. To suspend the write operation from the host to Compatible
FlashCopy S-VOLs by using consistency groups, you need to issue the pair creation command with
an option parameter.
When Compatible FlashCopy and Continuous Access Synchronous Z (Cnt Ac-S Z) share volumes,
the results of operations such as creating pairs will differ according to whether or not you are using
a consistency group.
Incremental FlashCopy function
Incremental FlashCopy maintains a relationship even after the copy operation from copy source
to target is completed. Later, when the S-VOL or T-VOL is updated, the updated data is managed
in a track as differential data. If the command to establish a relationship is re-executed on the
volumes originally related using the Incremental FlashCopy function, only differential data is copied.
12 About Compatible FlashCopy operations