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Quite often bees exceeds its service timeout for termination because it is waiting for a loop embedded in a Task to finish some long-running btrfs operation. This can cause bees to be aborted by SIGKILL before it can completely flush the hash table or save crawl state. There are only two important things SIGTERM does when bees terminates: 1. Save crawl progress 2. Flush out the hash table Everything else is automatically handled by the kernel when the process is terminated by SIGKILL, so we don't have to bother doing it ourselves. This can save considerable time at shutdown since we don't have to wait for every thread to reach a point where it becomes idle, or force loops to terminate by throwing exceptions, or check a condition every time we access a pointer. Instead, we need do only the things in the list above, and then call _exit() to clean up everything else. Hash table and crawl state writeback can happen in their background threads instead of the foreground one. Separate the "stop" method for these classes into "stop_request" and "stop_wait" so that these writebacks can run at the same time. Deprecate and remove all references to the BeesHalt exception, and remove several unnecessary checks for BeesContext::stop_requested. Pause the task queue instead of cancelling it, which preserves the crawl progress state and stops new Tasks from competing for iops and CPU during writeback. 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).