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What is the difference between the deduplication scan options “scan-old-data” and “scan-all”

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Applies to

  • ONTAP 9
  • AFF series

Answer

  • ONTAP’s deduplication process offers two scan options for efficiency and completeness:

-scan-old-data: Efficiently scans existing data, skipping shared (already deduplicated) blocks.

-scan-all: Performs a full scan, forcibly re-examining all blocks—including shared blocks.

  • Shared blocks are unique physical blocks referenced by multiple files or locations.
  • When deduplication has already occurred, shared blocks are not re-deduplicated by “scan-old-data,” but “scan-all” will re-examine all blocks, including those already deduplicated.

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