For general overview see here: BTRFS Compression.
Check zstd compression compression ratio using compsize:
$ sudo compsize $HOME
Processed 4521850 files, 6020362 regular extents (6190661 refs), 1797190 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 77% 945G 1.1T 1.1T
none 100% 800G 800G 797G
zstd 33% 144G 424G 429G
prealloc 100% 8.0K 8.0K 3.8MEnabling compression does not re-compress existing files. Instead you have to use btrfs filesystem defrag to re-compress them. To force recompression of existing data:
sudo btrfs fi defrag -v -czstd -r $HOMEStatistics after force compress:
$ sudo compsize $HOME
Processed 4521262 files, 5599695 regular extents (5599704 refs), 1797206 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 75% 931G 1.1T 1.1T
none 100% 778G 778G 778G
zstd 34% 152G 448G 448G
prealloc 100% 5.0M 5.0M 3.8MNote, normal compression has a feature in that if it detects that compression has little to no benefit. It doesn't bother continuing the compression for that particular file (thereby saving wasted CPU). By using compress-force, it attempts compression anyway. Good examples where this applies are for files that are already compressed (multimedia, zip files, etc). So the benefits might be limited. In previous case the savings are still noticeable.
See BRTFS Deduplication for details. rmlint is a duplicate file finder with btrfs support.
Example which finds duplicates for specific directory and generates shell script for deduplication.
rmlint -g -vv --types="duplicates" --config=sh:handler=clone $HOME
bash rmlint.sh
rm rmlint.shLinks