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Re: clearing 'flag unwritten extents'

To: Roger Willcocks <willcor@xxxxxxxxx>, Steve Lord <lord@xxxxxxx>
Subject: Re: clearing 'flag unwritten extents'
From: Nathan Scott <nathans@xxxxxxx>
Date: Wed, 16 Nov 2005 08:06:06 +1100
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <4379FDDE.2040807@xxxxxxx>; from lord@xxxxxxx on Tue, Nov 15, 2005 at 09:25:18AM -0600
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On Tue, Nov 15, 2005 at 09:25:18AM -0600, Steve Lord wrote:
> Roger Willcocks wrote:
> > On 11/13/05, Nathan Scott <nathans@xxxxxxx> wrote:
> >> On Fri, Nov 11, 2005 at 12:48:48PM +0000, Roger Willcocks wrote:
> >>> AIUI, the 'flag unwritten extents' option allows non-root users to
> >>> preallocate unwritten extents (root can always create them). Clearing
> >>> the option would just prevent the creation of new unwritten extents.
> >> It does more than just that - in xfs_bmapi it changes the way
> >> extents are handled - look for XFS_SB_VERSION_HASEXTFLGBIT in
> >> xfs_bmap.c in particular.
> > 
> > But only for realtime extents - and I don't have any of those...

Not only realtime - look more closely in xfs_bmapi().

> Nope, unwritten extents exist in the main part of the filesystem too.
> They are not always used, but they are not just for realtime files.

*nod*.  They are a Good Thing (tm), although the current code
implementing them on Linux is pretty horrible - that will get
alot better in the not-too-distant future.



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