Impossible compression ratio on ZFS

[Bruce Evans]

On Mon, 13 Jun 2011, [UTF-8] Å imun Mikecin wrote:

> 2011/6/13 Steven Hartland <killing at multiplay.co.uk>
>
>> Using 'du' for file sizes (without -A option) is wrong in the first place.
>>> Any program or script that is using it in such a way is broken and should
>>> be
>>> corrected.

You mean that any script that uses du with the -A option is broken.  -A
just shows the file size in bad units.

>> That's not true, -A displays the apparent size not the actual disk usage
>> which is what we want.
>
> Disk usage is not equal to file size. 'ls -al' shows file size, 'du' shows
> disk usage.
> Use the one you need, but don't expect them to be the same thing.

Indeed, the file size is only vaguely related to the disk usage.  Normal
du shows disk usage including increases of it due to metadata and
decreases of it due to compression or sparseness (which is a particular
type of compression).  du -A might be useful if the file is to be
copied to another file system with no compression at all.

Bruce