How to determine the reserved blocks in xfs filesystem ?

[Mukul Malhotra]

Thanks a lot for the solution.

​Mukul

On Wed, Nov 19, 2014 at 5:49 AM, Brian Foster <bfoster at redhat.com> wrote:

> On Wed, Nov 19, 2014 at 09:35:18AM +1100, Dave Chinner wrote:
> > On Tue, Nov 18, 2014 at 08:32:07AM -0500, Brian Foster wrote:
> > > On Tue, Nov 18, 2014 at 06:05:58PM +0530, Mukul Malhotra wrote:
> > > > ​Hello,
> > > >
> > > > Does xfs have reserved blocks too, like ext* ? if yes, how can they
> be
> > > > determined ?​
> > > >
> > >
> > > XFS reserves blocks internally such that it can perform operations when
> > > all free space is consumed, etc. It looks like 5% is the default.
> >
> > Not quite.
> >
> >         /*
> >          * We default to 5% or 8192 fsbs of space reserved, whichever is
> >          * smaller.  This is intended to cover concurrent allocation
> >          * transactions when we initially hit enospc. These each require
> a 4
> >          * block reservation. Hence by default we cover roughly 2000
> concurrent
> >          * allocation reservations.
> >          */
> >
> > So, in most cases, there are 32MB of reserved blocks available for
> > internal emergency use.
> >
>
> Yep, I glossed right over the hard cap... thanks. ;)
>
> Brian
>
> > > I don't think it's "like ext4," however, which reserves blocks for the
> > > root user. I don't believe the reserved blocks in XFS are accessible
> for
> > > file allocation by any user unless the reserve pool is modified as
> such.
> >
> > Most definitely not "like ext4". The reserved blocks are considered
> > "used space" (i.e. not available to any user) and are reported as
> > such in statfs() output (e.g. via df).
> >
> > Cheers,
> >
> > Dave.
> > --
> > Dave Chinner
> > david at fromorbit.com
>
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