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 should carefully
decide if you can tolerate not mirroring FlashCopy target volumes temporarily at a
remote site.
Multiple relationship FlashCopy
Multiple relationship FlashCopy allows a source volume to have multiple targets
simultaneously.
When a FlashCopy operation copies data from a source volume to a target volume,
that source volume can be involved in more than one FlashCopy relationship at the
same time (known as a multiple relationship FlashCopy). If a track on a volume is
not a target track of an existing FlashCopy relationship, it can become the target in
a new FlashCopy relationship. Up to twelve different target FlashCopy relationships
can exist for a single source volume.
If you require multiple copies of the same data, this function allows you to copy a
single source volume multiple (up to twelve) times to different target volumes as
soon as a FlashCopy volume is established. For example, suppose you use
FlashCopy to copy volume A to volume B. As soon as that FlashCopy relationship is
established, you can copy volume A to volume C. Once that relationship is
established, you can copy volume A to volume D, and so on. Multiple sessions
within a single volume are also possible.
Persistent FlashCopy
A persistent FlashCopy relationship is one that does not end when the background
physical copy ends. The relationship persists until explicitly withdrawn.
Persistent FlashCopy overrides normal FlashCopy processing and allows a
FlashCopy relationship to stay active until explicitly withdrawn. Generally, a
FlashCopy relationship is automatically withdrawn when the background physical
copy ends.
Designating that a FlashCopy relationship be persistent can help protect against
inadvertent updates of recently created target volumes. For example, if a source
volume is regularly copied to alternating target volumes (thereby ensuring that a
complete copy of the source volume is always available), the persistent relationship
will identify the target volume for the most recently completed FlashCopy.
Consider the following situation:
v A company wants to maintain more than one point-in-time copy version of a set
of its production volumes.
v The company creates a FlashCopy of its production volumes every eight hours,
each time using a different set of target volumes.
v The production volume is Volume A.
v The copies are Volume B, Volume C, and Volume D.
v The volumes that are copied contain a different point-in-time copy version.
The
following represents the procedure that FlashCopy operations follow in this
scenario:
Chapter 8. Optional feature codes for the DS8000 113
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