compsize takes a list of files (given as arguments) on a btrfs filesystem and measures used compression types and effective compression ratio, producing a report such as:
[~]$ compsize /usr/share
Processed 120101 files.
Type Perc Disk Usage Uncompressed
Data 58% 1.1G 1.9G
none 100% 351M 351M
zlib 29% 41M 137M
lzo 51% 776M 1.4G
A directory has no extents but has a (recursive) list of files. A non-regular file is silently ignored.
As it makes no sense to talk about compression ratio of a partial extent, every referenced extent is counted whole, exactly once -- no matter if you use only a few bytes of a 1GB extent or reflink it a thousand times. Thus, the uncompressed size will not match the number given by tar or du. On the other hand, the space used should be accurate (although obviously it can be shared with files outside our set).
The fields are:
- Perc: disk usage/uncompressed -- ie, effective compression ratio
- Disk Usage: blocks actually used on the disk
- Uncompressed: extents before compression
- Referenced: apparent size of files (minus holes)
The ioctl used requires root.
Besides regular C toolchain, you need btrfs userspace headers, usually installed as part of btrfs-progs. Required kernel: 3.16, btrfs-progs: 3.18 (untested!).