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SnapMirror storage efficiency configurations and behavior

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Applies to

  • ONTAP 9
  • SnapMirror
  • SnapVault

Answer

SnapMirror type-XDP relationships allow storage efficiency independence between source and destination volumes. While this allows for increased flexibility, certain combinations of storage efficiency settings can cause savings to be lost during transfer.

This KB is specific to SnapMirror type-XDP relationships. SnapMirror type-DP relationships maintain source-side storage efficiency savings by design but cannot have independent storage efficiency configurations on the destination volume.

Key:

  • D : Deduplication (Inline or background / post-process)
  • Ca : Adaptive Compression (Inline or postprocess)
  • Cs : Secondary Compression (Inline or postprocess)
  • "Logical Transfer with Storage Efficiency (LRSE)" : All source-side storage efficiency savings are maintained by SnapMirror.
  • "Logical Transfer (LRE)" : All source-side storage efficiency savings are lost during transfer, but can be re-gained at the destination.
Source Destination Result
D or No storage efficiency D or No additional storage efficiency Logical Transfer with Storage Efficiency (LRSE)
D, Ca or Cs D or No additional storage efficiency Logical Transfer with Storage Efficiency (LRSE)
D, Ca or Cs D, Ca or Cs Logical Transfer (LRE)
Any combination of storage efficiency Any storage efficiency including Ca or Cs Logical Transfer (LRE)
  • Any form of additional compression on a SnapMirror destination results in a non-storage efficient LRE transfer.
Data compaction
  • Data compaction has no impact on if LRSE or LRE are used by SnapMirror.
Source Destination Result
Data compaction enabled No data compaction Data compaction savings on source only
No data compaction Data compaction enabled Data compaction savings on destination only
Data compaction enabled Data compaction enabled Data compaction savings on both volumes*

*A SnapMirror destination will re-pack any compacted sub-4K chunks sent by the source. This may result in different (but similar) data compaction savings between source and destination volumes.

Extended compressed data
  • Extended compressed data is a combination of AFF or modern FAS platforms, ONTAP 9.5 or later, adaptive compression with application IO size 8K, and data compaction.
  • If a source volume uses Extended compressed data, the destination must be running ONTAP 9.5 or later for SnapMirror to maintain storage efficiency savings (LRSE), regardless of the destination's storage efficiency settings. If the destination is running ONTAP 9.4 or earlier, LRE will be used. For more details, see BUG 1277896.
  • Since extended compressed data includes adaptive compression, enabling on a SnapMirror destination volume will result in an LRE transfer.
Changing from LRE to LRSE
  • In ONTAP 9.3 and later, disabling all additional compression on a SnapMirror destination will allow transfers to switch from LRE to LRSE and start maintaining source-side storage efficiency savings. This is called Automatic LRE to LRSE.
  • Automatic LRE to LRSE takes two transfers to kick in after disabling compression at the destination.
  • Manual LRE to LRSE can also be attempted in ONTAP 9.3 and later using the -enable-storage-efficiency true option in a snapmirror update command.
LRE to LRSE conversion only works when compression types (adaptive or secondary) match between source and destination. If compression types are different, switching from LRE to LRSE is not possible. To achieve LRSE functionality, you must re-baseline to a new destination volume without additional compression enabled. To avoid a lengthy re-baseline, see the steps in  How to enable SnapMirror storage efficiency between volumes with different compression types.
  • Prior to ONTAP 9.3, switching from LRE to LRSE requires a re-baseline.
Other storage efficiency technologies
  • Aggregate deduplication (Cross-volume deduplication): Aggregate deduplication savings (inline or background / post-process) on a SnapMirror source are not retained by SnapMirror transfers. This has no impact to if LRSE or LRE are used. SnapMirror destination clusters can use aggregate deduplication with type-DP SnapMirror destination volumes. This also has no impact on if LRSE or LRE are used.

Additional Information

For more information on storage efficiency, see TR-4476.