Which mechanism ensures snapshot space efficiency by sharing unchanged blocks until modified?

• A. Data deduplication of blocks
• B. Inline compression of blocks
• C. Block-level mirroring for snapshots
• D. Copy-on-write

Answer: (D)

Copy-on-write is the mechanism that makes snapshots space-efficient by sharing unchanged blocks until they are modified. When a snapshot is created, it points to the same data blocks as the source volume. If the data remains unchanged, both the snapshot and the volume reference the same blocks, so no extra space is used. When a write happens to the volume after the snapshot, the system copies the original block and updates the working data to the new version, while the snapshot continues to reference the pre-modification block. This means only the blocks that are changed after the snapshot consume additional storage, keeping snapshot storage efficient.

Other options don’t provide this same behavior. Deduplication looks for identical blocks across the dataset but isn’t specifically about preserving historical data for snapshots; compression reduces the size of individual blocks rather than sharing blocks between the snapshot and the original; and block-level mirroring for snapshots isn’t the mechanism used to share blocks over time.