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PowerScale OneFS 9.2.1.0 CLI Administration Guide

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Defragmenter overview

The Small Files Storage Efficiency defragmenter reclaims space in the ShadowStore containers by moving data into a more optimal layout.

The defragmenter divides each SIN into logical chunks and assesses each chunk for fragmentation. If the current storage efficiency of each chunk is below a target efficiency then the chunk is processed by moving all of the data out of it and to another location where it is stored more efficiently.

The default target efficiency is 90% of the maximum storage efficiency available with the protection level used by the shadow store. Larger protection group sizes can tolerate a higher level of fragmentation before the storage efficiency drops below this threshold.

Attributes such as the chunk size, target efficiency, and the types of SINs to examine are configurable. In addition, you can configure the defragmenter to reduce the number of protection groups, when possible.

The defragmenter is implemented in the ShadowStoreDelete job. This job runs periodically to reclaim unused blocks from shadow stores. There is also a CLI command that runs the defragmenter.

The feature includes the following methods for obtaining statistics about fragmentation and storage efficiency. These aids can help you decide when and how often to run the defragmenter.

  • Running the defragmenter in assessment mode generates estimates of the amount of space that could be saved by defragmentation.
  • The isi_sstore list -v commmand generates fragmentation and storage efficiency scores.

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