Re: ENOSPC with mkdir and rename

[Hugo Mills <hugo@carfax.org.uk>]

[-- Attachment #1: Type: text/plain, Size: 1658 bytes --]

On Mon, Aug 04, 2014 at 11:48:17AM +0100, Peter Waller wrote:
> On 4 August 2014 11:39, Hugo Mills <hugo@carfax.org.uk> wrote:
> >> >  * btrfs fi df
> >> >     - look at metadata used vs total. If these are close to zero (on
> >> >       3.15+) or close to 512 MiB (on <3.15), then you are in danger of
> >> >       ENOSPC.
> >>
> >> Hmm. It's unfortunate that this could indicate an amount of space
> >> which is free when it actually isn't.
> >
> >    That's why the 512 MiB block reserve was split out of metadata --
> > so that you don't look at metadata and say "oh, I've got half a gig
> > free, that's OK".
> 
> I don't quite follow this. Is it a recent development I missed? When
> was it "split out"? More recently than the software I'm using?
> Otherwise I'm having difficulty parsing this.

   It's purely a change in the way that the kernel reports this info.
Before 3.15, the block reserve was included in the "Metadata" report
in btrfs fi df. After 3.15, the kernel reports the block reserve as
its own separate item in btrfs fi df (either as "BlockRsv", or
"unknown", depending on how old your userspace is). The theory is, the
change is made to make it clearer how much is used/reserved/free and
thus to make this kind of calculation simpler in the long run.

   Hugo.

-- 
=== Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk ===
  PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk
  --- Reading Mein Kampf won't make you a Nazi. Reading Das Kapital ---  
         won't make you a communist. But most trolls started out         
                    with a copy of Lord of the Rings.                    

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 811 bytes --]