Algorithms and Data Structures for Efficient Free Space Reclamation in WAFL


February 25, 2017


Ram Kesavan, Rohit Singh, and Travis Grusecki, NetApp; Yuvraj Patel, University of Wisconsin—Madison

15th USENIX Conference on File and Storage Technologies (FAST 2017) Feb. 27 - March 2, 2017 Santa Clara, CA.

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; failure to do so may impede allocations for incoming writes. Efficiency is also important, because the task may consume CPU and other resources. In this paper, we describe the evolution (over more than a decade) of WAFL’s algorithms and data structures for reclaiming space with minimal impact on the overall storage appliance performance.


The definitive version of the paper can be found at: