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How does Aggregate Deduplication affect SnapMirror?

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Applies to

  • SnapMirror
  • Aggregate-level deduplication
    • Aggregate deduplication
    • Cross-volume deduplication

Answer

  • Aggregate-level deduplication eliminates duplicate blocks across volumes belonging to the same aggregate
  • Aggregate deduplication savings (inline or background / post-process) on a SnapMirror source are not retained by SnapMirror transfers
    • This has no impact to SnapMirror maintaining volume-level storage efficiency savings from the source
  • SnapMirror destination clusters can use aggregate deduplication with type-DP SnapMirror destination volumes
    • This has no impact to SnapMirror maintaining volume-level storage efficiency savings from the source

Additional Information

Parent topic: SnapMirror storage efficiency configurations and behavior

To achieve cross-volume savings on a DP (Snapmirror destination) volume:

  1. Enable cross-volume-efficiency on the DP volume prior snapmirror initialize
  • Enable efficiency on the DP volume:
    volume efficiency on -vserver svm-destination -volume volume_dp
  • Enable cross-volume-background-dedupe on the DP volume:
    volume efficiency modify -vserver svm-destination -volume volume_dp -cross-volume-background-dedupe true
  • Initialize the Snapmirror relationship:
    snapmirror initialize -destination-vserver svm-destination -destination-volume volume_dp
  1. If Snapmirror re-initialize is not possible, a full-scan is required on the DP volume to initialize its block-fingerprint database:
  • This will take longer, because a full-scan takes a long time and can only consume limited CPU, so if possible prefer option 1
  • Enable efficiency on the DP volume:
    volume efficiency on -vserver svm-destination -volume volume_dp
  • Enable cross-volume-background-dedupe on the DP volume:
    volume efficiency modify -vserver svm-destination -volume volume_dp -cross-volume-background-dedupe true
  • Run a full-scan on the DP volume:
    volume efficiency start -vserver svm-destination -volume volume_dp -scan-old-data true
  • Wait for the full-scan to complete:
    volume efficiency show -vserver svm-destination -volume volume_dp -scan-old-data true -fields op-status
  1.  For SVM-DR, option 1 is not possible, because the volumes are only created during snapmirror initialize.
  • Use the same steps as in option 2, but make use of advanced command vserver config override for the non-show command:

set advanced

vserver config override -command "volume efficiency on -vserver svm-destination -volume volume_dp"

vserver config override -command "volume efficiency modify -vserver svm-destination -volume volume_dp -cross-volume-background-dedupe true"

vserver config override -command "volume efficiency start -vserver svm-destination -volume volume_dp -scan-old-data true"

With either option:

  • Cross-volume-savings are achieved after next aggregate efficiency background operation had triggered.
    • Check output from aggregate efficiency cross-volume-dedupe show to determine last operation end or current operational state
    • An aggregate efficiency background operation is triggered automatically upon a certain percentage of block-changes within the aggregate
    • An aggreate efficiency background operation can get trigegred manually using: aggregate efficiency cross-volume-dedupe start
  • An efficiency operation schedule for the DP volume efficiency operation is not required when LRSE (logical replication with storage efficiency) is in use.
  • With LRSE in use, every snapmirror update will trigger an efficiency background operation (only visible in sis.log) to achive cross volume savings.
  • The per-volume savings from the source-volume are maintained over from primary to secondary with XDP relatioonships using storage efficiency when there is no secondary compression enabled on the DP volume. Additional details:

 

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