The key difference between NetApp and other storage systems is …
Redirect on Write
NetApp FAS uses the techique after a snapshot being created. Any changes after a snapshot will be redirect to other available blocks, but not do any changes on the original data blocks.
Copy on First-Write
Other storage systems use this method to make a change after a snapshot being created. The first step to make a change is to read the original data block and copy it to the clone space. Then the new data is written in the original block. After all, the snapshot pointer will be changed to the cloned block.
The total operations for each block changing are 1 read and 3 write.