Describe the difference between Sync and Async SnapMirror replication.

• A. Async replication waits for commit on both source and destination; Sync replicates with a lag.
• B. Sync replication waits for commit on both source and destination; Async replicates with a lag.
• C. Sync replication is offline; Async is online.
• D. Sync uses snapshots; Async uses clones.

Answer: (B)

The difference lies in how commits are acknowledged and how data is kept in sync between the two sites. In synchronous replication, a write is not considered complete until it is durably committed on both the source and the destination. The destination must receive and persist the data before the operation is acknowledged, so the two ends stay in lockstep. This provides near-zero RPO and consistent recovery, but it adds latency and requires a reliable, high-bandwidth link.

In asynchronous replication, the write is acknowledged after it is committed on the source side, and the data is sent to the destination later in the background. The destination may lag behind the source, so there is a window of potential data loss if a failure occurs before replication catches up. This reduces write latency and network strain, making it suited for farther distances or where lower impact on production performance is desired, at the cost of higher RPO.