Re: Kernel 3.19 and still "disk full" even though 'btrfs fi df" reports enough room left?

[linux-btrfs.tebulin@xoxy.net]

This explanation helped a lot. Got it now!

Thank you!

>    You start with a load of unused space -- that's the "total" for
> each device in btrfs fi show. That space is allocated to specific
> usages as the FS needs it. The allocated space is the "used" in btrfs
> fi show for each device.
> 
>    Then we switch to looking at btrfs fi df. The "total" values are
> the amount of the *allocated* space given to each type of storage.
> Within those, actual stuff is stored (like your files), which is the
> "used" value for each kind of storage.
> 
>    If you've ever played SimCity, the allocation process is like
> zoning -- you say what kind of thing can go on the space, but it's not
> actually used until something gets built on it.
> 
>    The problem you hit is when everything has been allocated, and
> there's a need for more metadata space (usually), and there's lots of
> unused data space. The balance operation moves some things around so
> that some of the unused data allocation can be freed up, giving the FS
> the ability to allocate more metadata space.