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Re: direct-IO writes strange behavior

To: Alberto Nava <beto@xxxxxxxxxxx>
Subject: Re: direct-IO writes strange behavior
From: Steve Lord <lord@xxxxxxxx>
Date: 24 Nov 2003 14:36:24 -0600
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <3FC25E14.80001@xxxxxxxx>
Organization:
References: <3FBECF7E.6010509@xxxxxxxx> <3FBFEF6A.3000609@xxxxxxxxxxx> <3FC0EFEA.5070108@xxxxxxx> <3FC24602.5010904@xxxxxxxxxxx> <3FC25E14.80001@xxxxxxxxxxx>
Reply-to: lord@xxxxxxxx
Sender: linux-xfs-bounce@xxxxxxxxxxx
On Mon, 2003-11-24 at 13:37, Alberto Nava wrote:
> Alberto Nava wrote:
> 
> > 
> >> This may be an interaction with the unwritten extent handling code.
> >> Try this on a file system made with the mkfs option -d unwritten=0.
> >>
> > Thanks.
> > 
> > I tried it but made not difference. We got an unmapped bh and reverted 
> > to buffered-IO.
> opps.... It does work. I didn't preallocate enough space for the
> file as I was testing it. It works great now :-).
> 
> Are there any concerns when setting unwritten=0?

unwritten = 0 was the only supported mode on linux (and originally irix)
for a long time. The issue was that using preallocation meant you could
go read old data off the disk. On linux now an unwritten=0 filesystem
should restrict the preallocation calls to root.

Steve
-- 
Steve Lord <lord@xxxxxxx>


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