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How ARP creates Snapshots

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Answer

Options default value:
  • arw.snap.create.interval.hours = 4 hours
  • arw.snap.new.extns.interval.hours = 48 hours (Beginning with ONTAP 9.13)
A snapshot for new-extension is created if all conditions below are true:
  1. The last high-entropy snapshot is more than 30 minutes old.
  2. The last new-extension snapshot is more than 4 hours old. 
  3. The last new-extension snapshot is more than 48 hours old. (Beginning with ONTAP 9.13)
Scenario-1: Only high-entropy data. No new file extension.
  • T: Snapshot created due to high-entropy data.
  • T + 4 hour: Snapshot created due to high-entropy data.
  • T + 8 hour: Snapshot created due to high-entropy data.
  • T + 12 hour: Snapshot created due to high-entropy data.
  • …
Scenario-2: High-entropy data and new file extensions. 

Note: The further description refers to reasons a and b above.

  • ONTAP 9.10, 9.11, 9.12:
    • T: Snapshot created due to high-entropy data.
    • T + 20 mins: A new file extension .abcd with 20+ files observed. Snapshot not created for reason a.
    • T + 30 mins: A new file extension .efgh with 20+ files observed. Snapshot created. (The next snapshot for new-extension will not be created until 4 hours from this point)
    • T + 40 mins: A new file extension .ijkl with 20+ files observed. Snapshot not created for reason b.
    • T + 2 hours: A new file extension .mnop with 20+ files observed. Snapshot not created for reason b.
    • T + 4 hours: Snapshot created due to high-entropy data.
    • T + 5 hours: A new file extension .qrst with 20+ files observed. Snapshot created  (The next snapshot for new-extension will not be created until 4 hours from this point)
    • T + 8 hours: Snapshot created due to high-entropy data.
    • …
  • ONTAP 9.13 or later:
    • T: Snapshot created due to high-entropy data.
    • T + 20 mins: A new file extension .abcd with 20+ files observed. Snapshot not created for reason a.
    • T + 30 mins: A new file extension .efgh with 20+ files observed. Snapshot created. (The next snapshot for new-extension will not be created until 48 hours from this point)
    • T + 40 mins: A new file extension .ijkl with 20+ files observed. Snapshot not created for reason c.
    • T + 2 hours: A new file extension .mnop with 20+ files observed. Snapshot not created for reason c.
    • T + 4 hours: Snapshot created due to high-entropy data.
    • T + 5 hours: A new file extension .qrst with 20+ files observed. Snapshot not created for reason c.
    • T + 8 hours: Snapshot created due to high-entropy data.
    • …
    • T + 48 hours: Snapshot created due to high-entropy data.
    • T + 48 hours + 20 mins: A new file extension .uvwx with 20+ files observed. Snapshot not created for reasons a & c.
    • T + 48 hours + 30 mins: A new file extension .wxyz with 20+ files observed. Snapshot created. (The next snapshot for new-extension will not be created until 48 hours from this point)

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