B-trees, shadowing, and clones

Abstract

B-trees are used by many file systems to represent files and directories. They provide guaranteed logarithmic time key-search, insert, and remove. File systems like WAFL and ZFS use shadowing, or copy-on-write, to implement snapshots, crash recovery, write-batching, and RAID. Serious difficulties arise when trying to use b-trees and shadowing in a single system.

This article is about a set of b-tree algorithms that respects shadowing, achieves good concurrency, and implements cloning (writeable snapshots). Our cloning algorithm is efficient and allows the creation of a large number of clones.

We believe that using our b-trees would allow shadowing file systems to better scale their on-disk data structures.

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Index Terms

• General and reference

  • Cross-computing tools and techniques

    • Performance

• Information systems

  • Information storage systems

    • Storage management

• Software and its engineering

  • Software organization and properties

    • Contextual software domains

      • Operating systems

        • File systems management

        • Memory management

    • Extra-functional properties

      • Software performance