IBM DS8000 - ADDITIONAL INFORMATION, User Manual, Page: 138 / 250

FlashCopy to Metro Mirror source volumes
You can use an existing Metro Mirror source volume as a FlashCopy target
volume. This process allows you to create a point-in-time copy and then make a
copy of that data at a remote site.
Previously, you could create a FlashCopy relationship between two volumes and
then create a Metro Mirror volume pair by using the FlashCopy target volume as
the Metro Mirror source volume. However, you could not use an existing Metro
Mirror source volume as a FlashCopy target volume. This is no longer a restriction.
You can create FlashCopy target volumes that serve as production volumes and
mirror them to a remote site using the Metro Mirror function.
You can create a full volume or incremental point-in-time copy to an existing
Metro Mirror source volume. The first time that you create a FlashCopy operation,
the entire Metro Mirror source volume has to be copied to the remote site, similar
to a new pair being established. Afterwards, provided that you created the
FlashCopy volume pair with the persistent and change recording options, you can
perform a refresh (incremental) operation of the FlashCopy relationship. The
refresh operation copies only changes and sends them to the remote site, requiring
less time for the remote mirror and copy volumes to be synchronized again.
When you create a FlashCopy operation and the logical copy finishes, the
corresponding Metro Mirror volume pairs turn to the duplex pending status as
long as the FlashCopy data is being transferred to the Metro Mirror remote site.
The time it takes to complete the copy of the FlashCopy data, until all remote
mirror and copy volumes are synchronous again, depends on the amount of data
to be transferred and the available bandwidth to the remote site. Be aware that,
during this time, the remote site will be inconsistent if a disaster occurs. Therefore,
you must carefully decide if you can tolerate not mirroring FlashCopy target
volumes temporarily at a remote site.
FlashCopy initiated from Volume A to
Volume B.
olumes.
Change recording starts
on both v
Once FlashCopy is established, the
P-i-T copy is available, and Volume A
and Volume B can start receiving updates
Background copy task copies data
from Volume A to Volume B.
Reverse restore initiated from
Volume B to Volume A:
Background copy task copies
from Volume B
and Volume A to Volume A.
updated tracks
Change recording reset to track
new changes (ready for the next
incremental FlashCopy request).
Time
volume A
volume A
volume A
volume A
volume B
volume B
volume B
volume B
1tyt
ax
Figure 10. Refreshing target volume — reverse restore
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DS8000 User’s Guide