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What is the recommended volume size relative to LUN size when creating LUNs in ONTAP?

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ontap-9
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san
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Applies to

ONTAP 9

Answer

  • LUN size must be less than or equal to the volume size.
  • ONTAP reserves space in the volume for internal metadata, WAFL file system overhead, and Snapshot copies.
  • Creating a LUN with a size equal to the volume size can cause errors such as No space left on device during LUN creation or data writes.
  • Sufficient free space is required for: 
    • Metadata and WAFL file system overhead
    • Snapshot copies (if enabled)
    • Other management operations
  • Recommended best practice: 
    • Set LUN size 5–10% smaller than the volume size.
    • Example: For a 10 TB volume, configure a LUN of up to 9.5 TB.
  • If using thin provisioning (space guarantee none), ensure sufficient available physical space on the aggregate to avoid write failures.
  • Insufficient free space can lead to: 
    • Write errors
    • Snapshot failures
    • LUN offline situations

Additional Information

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