Storage

Tracking Back References in a Write-Anywhere File System

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Executive Summary

Many file systems reorganize data on disk, for example to defragment storage, shrink volumes, or migrate data between different classes of storage. Advanced file system features such as snapshots, writable clones, and deduplication make these tasks complicated, as moving a single block may require finding and updating dozens, or even hundreds, of pointers to it. The authors present Backlog, an efficient implementation of explicit back references, to address this problem. Back references are file system meta-data that map physical block numbers to the data objects that use them.

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