Re: What to do about df and btrfs fi df

[Goswin von Brederlow <goswin-v-b@web.de>]

On Mon, Feb 17, 2014 at 06:08:20PM +0100, David Sterba wrote:
> On Mon, Feb 10, 2014 at 01:41:23PM -0500, Josef Bacik wrote:
> > 
> > 
> > On 02/10/2014 01:36 PM, cwillu wrote:
> > >IMO, used should definitely include metadata, especially given that we
> > >inline small files.
> > >
> > >I can convince myself both that this implies that we should roll it
> > >into b_avail, and that we should go the other way and only report the
> > >actual used number for metadata as well, so I might just plead
> > >insanity here.
> > >
> > 
> > I could be convinced to do this.  So we have
> > 
> > total: (total disk bytes) / (raid multiplier)
> > used: (total used in data block groups) +
> > 	(total used in metadata block groups)
> > avail: total - (total used in data block groups +
> > 		total metadata block groups)
> 
> The size of global block reserve should be IMO subtracted from 'avail',
> this reports the space as free, but is in fact not.

How much global block reserve is there? Does that explain why I can't
use the last 270G of my 19TB btrfs?
 
> The "used" amount of the global reserve might be included into
> filesystem 'used', but I've observed the global reserve used for short
> periods of time under some heavy stress, I'm convinced it needs to be
> accounted in the df report.

As a comparison the ext2/3/4 filesystem has a % reserved for root and
does not show this in available. So you get filesystem with 0 bytes
free but root can still write to them.

I would argue that available should not include the reserve. It is not
available for normal operations, right?

MfG
	Goswin