Incremental flashcopy function – HP XP Business Copy Software User Manual

Page 107

Figure 52

Ex. Consist. Group w/FlashCopy(R) Mirror Ver. 2: Copying Mult. Data Stored over Mult. Vols.

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,

, 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 ”

” on page 132. For the information about the example of using the

command, see ”

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,

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

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