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Why doesn't the used space decrease by the same amount on ONTAP after deleting data?

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Category:
ontap-9
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core
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Applies to

  • ONTAP 9
  • WAFL (Write Anywhere File Layout) file system
  • Snapshot functionality
  • Data deduplication and compression

Answer

When data is deleted from a Windows system, the expected decrease in storage size may not be immediately reflected in ONTAP due to several factors:
  • Snapshot Existence:
In ONTAP, if the Snapshot feature is enabled, deleted files are retained within the Snapshots.
This means that even though files are deleted from the Windows side, they are logically deleted but physically retained in Snapshots on the NetApp system.
  • WAFL File System Characteristics:
The WAFL file system used by ONTAP does not immediately release metadata or blocks associated with deleted files.
This delayed release can cause a discrepancy in the reported storage capacity.
  • Impact of Deduplication and Compression:
The storage capacity reported by ONTAP includes the effects of deduplication and compression.
As a result, the size of deleted data on Windows may differ from the size reported on ONTAP due to these storage efficiency processes.
  • Reflection Timing After Large Data Deletion:
When large volumes of data are deleted, ONTAP may take time to process and reflect these changes due to the data consistency operations.
This delay can result in a temporary mismatch between the expected and reported storage usage.

Additional Information

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