HP XP7 Storage - Manual (Page 13)

Figure 8 Using Consistency Groups with Compatible FlashCopy: Copying multiple data stored over
multiple volumes
The first figure shows copying the data stored on volumes #1-#3 to volumes #4-#6. You need to
establish relationships for 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 (relationship 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 a
single consistency group, and enables you to suspend the write operation from the host to the
Compatible FlashCopy S-VOLs until Relationship A, Relationship B, and Relationship C are all
created and all copy 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 relationship
creation command with the appropriate “freeze” option parameter for your interface.
When Compatible FlashCopy and Continuous Access Synchronous Z (Cnt Ac-S Z) share volumes,
the results of operations such as creating pairs and relationships will differ according to whether
or not you are using a consistency group.
Incremental FlashCopy function (Compatible FlashCopy only)
Incremental FlashCopy maintains a relationship even after the copy operation from copy source
to target is completed. After the background copy completes, when the S-VOL or T-VOL is updated,
the location of the updated data is managed using differential bitmaps. 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. The following figure shows the workflow from establishing
the relationship (using Compatible FlashCopy) to executing the update copy operation using the
Incremental FlashCopy function.
Incremental FlashCopy function (Compatible FlashCopy only) 13