Efficient Search for Free Blocks in the WAFL File System

Ram Kesavan, Matthew Curtis-Maury, and Mrinal Bhattacharjee (NetApp)

47th International Conference on Parallel Processing (ICPP 2018)
August 13-16, 2018 Eugene, Oregon, USA

The WAFL write allocator is responsible for assigning blocks on persistent storage to data in a way that maximizes both write throughput to the storage media and subsequent read performance of data. The ability to quickly and efficiently guide the write allocator toward desirable regions of available free space is critical to achieving that goal. This ability is influenced by several factors, such as any underlying RAID geometry, media-specific attributes such as erase-block size of solid state drives or zone size of shingled magnetic hard drives, and free space fragmentation. This paper presents and evaluates the techniques used by the WAFL write allocator to efficiently find regions of free space.

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