Which replication method requires the LEAST amount of space?

A copy implies creating a full, independent duplicate of the data, requiring an amount of space equal to the original data.

A clone is a full, independent duplicate of a virtual disk or volume at a specific point in time, requiring an amount of space equal to the original data.

A snapshot is a point-in-time reference to data, typically storing only the changes made to the original data block-level, rather than a full duplicate. This "copy-on-write" or similar mechanism means it initially consumes very little space, growing only as data changes.

A mirror creates and maintains a real-time, identical duplicate of data on a separate storage device, consuming an amount of space equal to the original data.