Which feature of WAFL enables copy-on-write functionality?

• A. Copy-on-write semantics
• B. Snapshot management
• C. Data replication
• D. Data compression

Answer: (A)

Copy-on-write semantics is the mechanism that makes copy-on-write functionality possible in WAFL. In WAFL, when data is changed, the system writes the new data to fresh blocks rather than overwriting the existing ones. Pointers in the metadata are then updated to reference these new blocks, while the old blocks remain intact for any existing references, such as snapshots. This is what allows instant, consistent point-in-time images without duplicating data. Snapshot management leverages this behavior to create and manage images, but the actual capability to perform copy-on-write comes from the semantics themselves. Data replication and data compression are separate features and do not enable the copy-on-write mechanism.