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# compsize
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 /home
Processed 140058 files, 133128 regular extents (196786 refs), 80886 inline.
Type Perc Disk Usage Uncompressed Referenced
TOTAL 93% 14G 15G 12G
none 100% 13G 13G 10G
zlib 41% 628M 1.4G 1.4G
zstd 28% 42M 148M 148M
```
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:
* Type: compression algorithm used
* 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.
# Installation:
Besides regular C toolchain, you need btrfs userspace headers. On Debian
(incl. derivatives like Ubuntu) they're in libbtrfs-dev, SuSE ships them
inside libbtrfs-devel, they used to come with btrfs-progs before.
Required kernel: 3.16, btrfs-progs: 3.18 (untested!).
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