Chapter 3. Data management features
The DS8000 storage unit is designed with many management features that allow
you to securely process and access your data according to your business needs,
even if it is 24 hours a day and 7 days a week.
This chapter contains information about the data management features in your
DS8000. Use the information in this chapter to assist you in planning, ordering
licenses, and in the management of your DS8000 data management features.
FlashCopy SE feature
The FlashCopy SE feature allocates storage space on an as-needed basis by using
space on a target volume only when it actually copies tracks from the source
volume to the target volume.
Without track space-efficient (TSE) volumes, the FlashCopy function requires that
all the space on a target volume be allocated and available even if no data is
copied there. With space-efficient volumes, FlashCopy uses only the number of
tracks that are required to write the data that is changed during the lifetime of the
FlashCopy relationship, so the allocation of space is on an as-needed basis. Because
it does not require a target volume that is the exact size of the source volume, the
FlashCopy SE feature increases the potential for a more effective use of system
storage capacity.
FlashCopy SE is intended for temporary copies. Unless the source data has little
write activity, copy duration does not last longer than 24 hours. The best use of
FlashCopy SE is when less than 20% of the source volume is updated over the life
of the relationship. Also, if performance on the source or target volumes is
important, standard FlashCopy is strongly recommended.
You can define the space-efficiency attribute for the target volumes during the
volume creation process. A space-efficient volume can be created from any extent
pool that has space-efficient storage already created in it. Both the source and
target volumes of any FlashCopy SE relationship must be on the same server
cluster.
If the space-efficient source and target volumes have been created and are
available, they can be selected when you create the FlashCopy relationship.
Important: Space-efficient volumes are currently supported as FlashCopy target
volumes only.
After a space-efficient volume is specified as a FlashCopy target, the FlashCopy
relationship becomes space-efficient. FlashCopy works the same way with a
space-efficient volume as it does with a fully provisioned volume. All existing copy
functions work with a space-efficient volume except for the Background Copy
function (not permitted with a space-efficient target) and the Dataset Level
FlashCopy function. A miscalculation of the amount of copied data can cause the
space-efficient repository to run out of space, and the FlashCopy relationship fails
(that is, reads or writes to the target are prevented). You can withdraw the
FlashCopy relationship to release the space.
© Copyright IBM Corp. 2004, 2012 41
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