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24b08ef7b7
A laundry list of problems fixed: * Track which physical blocks have been read recently without making any changes, and don't read them again. * Separate dedupe, split, and hole-punching operations into distinct planning and execution phases. * Keep the longest dedupe from overlapping dedupe matches, and flatten them into non-overlapping operations. * Don't scan extents that have blocks already in the hash table. We can't (yet) touch such an extent without making unreachable space. Let them go. * Give better information in the scan summary visualization: show dedupe range start and end points (<ddd>), matching blocks (=), copy blocks (+), zero blocks (0), inserted blocks (.), unresolved match blocks (M), should-have-been-inserted-but-for-some-reason-wasn't blocks (i), and there's-a-bug-we-didn't-do-this-one blocks (#). * Drop cached data from extents that have been inserted into the hash table without modification. * Rewrite the hole punching for uncompressed extents, which apparently hasn't worked properly since the beginning. Nuisance dedupe elimination: * Don't do more than 100 dedupe, copy, or hole-punch operations per extent ref. * Don't split an extent or punch a hole unless dedupe would save at least half of the extent ref's size. * Write a "skip:" summary showing the planned work when nuisance dedupe elimination decides to skip an extent. Signed-off-by: Zygo Blaxell <bees@furryterror.org>
BEES
Best-Effort Extent-Same, a btrfs deduplication agent.
About bees
bees is a block-oriented userspace deduplication agent designed for large btrfs filesystems. It is an offline dedupe combined with an incremental data scan capability to minimize time data spends on disk from write to dedupe.
Strengths
- Space-efficient hash table and matching algorithms - can use as little as 1 GB hash table per 10 TB unique data (0.1GB/TB)
- Daemon incrementally dedupes new data using btrfs tree search
- Works with btrfs compression - dedupe any combination of compressed and uncompressed files
- Works around btrfs filesystem structure to free more disk space
- Persistent hash table for rapid restart after shutdown
- Whole-filesystem dedupe - including snapshots
- Constant hash table size - no increased RAM usage if data set becomes larger
- Works on live data - no scheduled downtime required
- Automatic self-throttling based on system load
Weaknesses
- Whole-filesystem dedupe - has no include/exclude filters, does not accept file lists
- Requires root privilege (or
CAP_SYS_ADMIN) - First run may require temporary disk space for extent reorganization
- First run may increase metadata space usage if many snapshots exist
- Constant hash table size - no decreased RAM usage if data set becomes smaller
- btrfs only
Installation and Usage
Recommended Reading
- bees Gotchas
- btrfs kernel bugs - especially DATA CORRUPTION WARNING
- bees vs. other btrfs features
- What to do when something goes wrong
More Information
Bug Reports and Contributions
Email bug reports and patches to Zygo Blaxell bees@furryterror.org.
You can also use Github:
https://github.com/Zygo/bees
Copyright & License
Copyright 2015-2023 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).