A copy-on-write operation occurs the first time any data block is modified on the base logical drive
Since the FlashCopy repository logical drive stores copies of the original data in those data blocks, further changes to those data blocks write directly to the base logical drive without another copy-on-write. And, since the only data blocks that are physically stored in the FlashCopy repository logical drive are those that have changed since the time of the FlashCopy, the FlashCopy technology uses less disk space than a full physical copy.
For more information, see Introduction to FlashCopy Logical Drives on the Learn More tab.