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Why does used size of lun show different than used size from lun host ?

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Category:
ontap-9
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san
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Applies to

  • ONTAP 9
  • SAN

Answer

  • It's a expected behavior where the LUN is hosted on space guaranteed volume.
  • The space discrepancy is caused by thick provisioning being enabled on both the volume and the LUN on storage end.
  • Thick-provisioned LUNs reserve space for the entire LUN size, regardless of how much data is actually written.
  • Thick-provisioned volumes (space guarantee = volume) reserve space for the full volume size and include the space reserved for the LUN, plus any additional overhead (such as WAFL metadata, snapshots, or other files).
  • As a result, ONTAP reports the “used” space on the volume as the total reserved space, which can be much higher than the actual data written to the LUN.

Additional Information

  • If LUN space reclaim enabled on storage side and is supported by the client OS, then the used size of lun show is approximately the same as the used space seen on the host.
  • What does the LUN option space_alloc do?
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