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When two Tasks attempt to lock the same extent, append the later Task to the earlier Task's post-exec work queue. This will guarantee that all Tasks which attempt to manipulate the same extent will execute sequentially, and free up threads to process other extents. Similarly, if two scanner threads operate on the same inode, any dedupe they perform will lock out other scanner threads in btrfs. Avoid this by serializing Task objects that reference the same file. This does theoretically use an unbounded amount of memory, but in practice a Task that encounters a contended extent or inode quickly stops spawning new Tasks that might increase the queue size, and all Tasks that might contend for the same lock(s) end up on a single FIFO queue. Note that the scope of inode locks is intentionally global, i.e. when an inode is locked, it locks every inode with the same number in every subvol. This avoids significant lock contention and task queue growth when the same inode with the same file extents appear in snapshots. Fixes: https://github.com/Zygo/bees/issues/158 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
- NEW Works around
btrfs sendproblems with dedupe and incremental parent snapshots - 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 2015-2022 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).