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The Linux kernel's btrfs headers are better than the libbtrfs-dev headers: - the libbtrfs-dev headers have C++ language compatibility issues - upstream version in Linux kernel is more accurate and up to date - macros in libbtrfs-dev's ctree.h hide information that would enable bees to perform runtime buffer length checking - enum types whose presence cannot be detected with #ifdef When accessing members of metadata items from the filesystem, we want to verify that the member we are accessing is within the boundaries of the item that was retrieved; otherwise, a memory access violation may occur or garbage may be returned to the caller. A simple C++ template, given a pointer to a structure member and a buffer, can determine that the buffer contains enough bytes to safely access a struct member. This was implemented back in 2016, but left unused due to ctree.h issues. Some btrfs metadata structures have variable length despite using a fixed-size in-memory structure. The members that appear earliest in the structure contain information about which following members of the structure are used. The item stored in the filesystem is truncated after the last used member, and all following members must not be accessed. 'btrfs_stack_*' accessor macros obscure the memory boundaries of the members they access, which makes it impossible for a C++ template to verify the memory access. If the template checks the length of the entire structure, it will find an access violation for variable-length metadata items because the item is rarely large enough for the entire structure. Get rid of all the libbtrfs-dev accessor macros and reimplement them with the necessary buffer length checks. 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 shapshots - 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 2015-2018 Zygo Blaxell bees@furryterror.org.
GPL (version 3 or later).