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We detect toxic extents by measuring how long the LOGICAL_INO ioctl takes to run. If it is above some threshold, we consider the extent toxic, and blacklist it; otherwise, we process the extent normally. The detector was using the execution time of the ioctl, which detects toxic extents, but it also detects pauses of the bees process and transaction commit latency due to load. This leads to a significant number of false positives. The detection threshold was also very long, burning a lot of kernel CPU before the detection was triggered. Use the per-thread system CPU statistics to measure the kernel CPU usage of the LOGICAL_INO call directly. This is much more reliable because it is not confounded by other threads, and it's faster because we can set the time threshold two orders of magnitude lower. Also remove the lock and mutex added in "context: serialize LOGICAL_INO calls" because we theoretically no longer need it (but leave the code there with #if 0 in case we do need it in practice). 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)
- Incremental realtime dedupe of 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
- Runs continuously as a daemon - no quick start/stop
- 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
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 2015-2018 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).