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What is the object fragmentation in fabricpool?

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ontap-9
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core
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Applies to

  • Ontap 9
  • Fabricpool tiering

Answer

  • FabricPool does not delete blocks from attached object stores.
  • Instead, FabricPool deletes entire objects after a certain percentage of the blocks in the object are no longer referenced by ONTAP.
    • For example, there are 1,024 4KB blocks in a 4MB object tiered to Amazon S3.
  • If a customer/client app makes a delete or a write to a file that has cold blocks in an object, the cold block becomes unreferenced, but it stays in the object.
    • This fragmentation slowly builds up until it crosses the unreclaimed space threshold and we delete the object and fold any existing referenced blocks into a new object.
  • Defragmentation and deletion do not occur until less than 205 4KB blocks (20% of 1,024) are being referenced by ONTAP.
    • When enough (1,024) blocks have zero references, their original 4MB objects are deleted, and a new object is created.

More details available in TR-4598.

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