IBM TotalStorage DS300 Best Practices Manual page 189

Figure 4-151 Array with logical drive and data
A Flashcopy of an existing logical drive is created by using the snapshot
command in the command line interface. The process of creating the Flashcopy
includes the creation of a new logical drive in the same array than the source
logical drive. The target logical drive will have 10% of the capacity of the source
logical drive. It contains two data regions. One region is used for changed data
on the source logical drive and the other region is used for a lookup table. The
lookup table maintains a relationship between the data blocks of the source and
target logical drive. There are no data block in the target logical drive at this time.
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Chapter 4. TotalStorage DS300 and DS400 management