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Re: How to determine the reserved blocks in xfs filesystem ?

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: How to determine the reserved blocks in xfs filesystem ?
From: Mukul Malhotra <smilemukul2005@xxxxxxxxx>
Date: Fri, 21 Nov 2014 22:06:35 +0530
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
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Thanks a lot for the solution.

âMukul

On Wed, Nov 19, 2014 at 5:49 AM, Brian Foster <bfoster@xxxxxxxxxx> 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:
> > > âHello,
> > >
> > > Does xfs have reserved blocks too, like ext* ? if yes, how can they be
> > > determined ?â
> > >
> >
> > 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.
>
>Â Â Â Â Â/*
>Â Â Â Â Â * We default to 5% or 8192 fsbs of space reserved, whichever is
>     * smaller. This is intended to cover concurrent allocation
>Â Â Â Â Â * transactions when we initially hit enospc. These each require a 4
>Â Â Â Â Â * block reservation. Hence by default we cover roughly 2000 concurrent
>Â Â Â Â Â * allocation reservations.
>Â Â Â Â Â */
>
> 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@xxxxxxxxxxxxx

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