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What is an example how SnapMirror lag time is calculated?

Last Updated:

Applies to

  • ONTAP 9
  • SnapMirror


  • Scenario 1   
    Source  Destination
    ControllerA:vol_1 ControllerB:vol_1_mir
  1. A scheduled update starts at 12:00pm
  2. A SnapMirror snapshot is created on the Source volume, and a transfer is started 
  3. The transfer takes 45 minutes to complete
  4. The time on the destination system is now 12:46pm
  5. The transfer completed 1 minute ago

If measured during step 5, the lag is 46 minutes, because:

  • 46 minutes have elapsed since the snapshot was created on the source
  • 46 minutes elapsed since the snapshot was successfully transferred to the destination
  • On the Destination, Lag is calculated by finding the difference between:
    • The snapshot creation timestamp
    • The time on the destination, based on the destination storage controller's clock 
    • If the time is not configured correctly on the destination or source, the lag time will be incorrect
  • Scenario 2
    Primary Secondary
    CIFS_SVM:vol_1 CIFS_DR:vol_1_dr
  1. Based on the snapshot policy on vol_1, a snapshot is created at 5pm
  2. The snapshot is created with the snapmirror-label sv_daily
  3. At 1 AM the following morning, a scheduled snapmirror update is triggered, configured to replicate any snapshot labeled sv_daily
  4. The transfer takes 30 minutes to complete

The lag in this scenario would be 8 hours 30 minutes, because:

  • At the time of the scheduled snapmirror update, eight hours had elapsed since the snapshot was created and labeled sv_daily
  • Transferring the snapshot from the source to the destination took 30 minutes


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