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118 DS8000 Series: Concepts and Architecture
– If the backup data is not copied yet, first the backup data is copied to the target volume,
and after that it is updated on the source volume.
Write to the target volume
When you write some data to the target volume, it is written to the data cache and
persistent memory, and FlashCopy manages the bitmaps to not overwrite the latest data.
FlashCopy does not overwrite the latest data by the physical copy.
The background copy may have a slight impact to your application because the physical copy
needs some storage resources, but the impact is minimal because the host I/O is prior to the
background copy. And if you want, you can issue FlashCopy with the
no background copy
option.
No background copy option
If you invoke FlashCopy with the no background copy option, the FlashCopy relationship is
established without initiating a background copy. Therefore, you can minimize the impact of
the background copy. When the DS8000 receives an update to a source track in a FlashCopy
relationship, a copy of the point-in-time data is copied to the target volume so that it is
available when the data from the target volume is accessed. This option is useful for
customers who don’t need to issue FlashCopy in the opposite direction.
Benefits of FlashCopy
The point-in-time copy created by FlashCopy is typically used where you need a copy of the
production data to be produced with little or no application downtime (depending on the
application). It can be used for online backup, testing of new applications, or for creating a
database for data-mining purposes. The copy looks exactly like the original source volume
and is an instantly available, binary copy.
Point-in-Time Copy function authorization
FlashCopy is an optional function. To use it, you must purchase the Point-in-Time Copy 2244
function authorization model, which is 2244 Model PTC.
7.2.2 FlashCopy options
FlashCopy has many options and expanded functions to help provide data duplication. We
explain these options and functions in this section.
Refresh target volume (also known as Incremental FlashCopy)
Refresh target volume provides the ability to refresh a LUN or volume involved in a FlashCopy
relationship. When a subsequent FlashCopy operation is initiated, only the tracks changed on
both the source and target need to be copied from the source to the target. The direction of
the
refresh can also be reversed.
In many cases, at most 10 to 20 percent of your entire data is changed in a day. In such a
situation, if you use this function for daily backup, you can save the time for the physical copy
of FlashCopy.
Figure 7-2 on page 119 explains the architecture for Incremental FlashCopy.