Efficient Free Space Reclamation in WAFL

Ram Kesavan, Rohit Singh, Travis Grusecki, Yuvraj Patel

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

NetApp®WAFL® is a transactional file system that uses the copy-on-write mechanism to support fast write performance and efficient snapshot creation. However, copy-on-write increases the demand on the file system to find free blocks quickly, which makes rapid free space reclamation essential. Inability to find free blocks quickly may impede allocations for incoming writes. Efficiency is also important, because the task of reclaiming free space may consume CPU and other resources at the expense of client operations. In this article, we describe the evolution (over more than a decade) of the WAFL algorithms and data structures for reclaiming space with minimal impact to the overall performance of the storage appliance.
Original languageEnglish
Article number23
Number of pages29
JournalTransactions on Storage (TOS)
Issue number3
Publication statusPublished - 28 Sept 2017

Keywords / Materials (for Non-textual outputs)

  • Storage system
  • snapshots
  • garbage collection
  • file system performance
  • free space reclamation
  • file system
  • deduplication


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