Which mechanism does ONTAP use to maintain cache coherency across FlexCache and origin when changes occur?

• A. File-level invalidation messaging to mark stale data when changes occur.
• B. Periodic polling of the origin for changes.
• C. Client-side timeouts to detect staleness.
• D. Metadata versioning to track changes.

Answer: (A)

The mechanism hinges on timely, precise invalidation of cached data. When the origin data changes, ONTAP sends file-level invalidation messages to the FlexCache, marking the affected cached files or blocks as stale. This forces subsequent reads to fetch updated data from the origin (or refresh the cached copy), ensuring readers don’t see out-of-date content. This per-file invalidation provides immediate, fine-grained coherence and scales well across multiple clients.

Other approaches like periodic polling would risk serving stale data between polls and add extra load; client-side timeouts rely on each client to detect staleness without a centralized coherence signal; and metadata versioning alone doesn’t automatically invalidate cached content across all clients. Therefore, file-level invalidation messaging is the appropriate, effective method for maintaining cache coherency in FlexCache.