> -----Original Message-----
> From: Timothy Shimmin [mailto:tes@xxxxxxx]
> Sent: Thursday, February 15, 2007 3:19 AM
> To: Leon Kolchinsky; linux-xfs@xxxxxxxxxxx
> Subject: Re: mkfs and mount tips?
>
> Hi Leon,
>
> --On 13 February 2007 10:48:15 AM +0200 Leon Kolchinsky
> <leonk@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> > I've also seen "–d unwritten=0" option:
> >
> > So my question:
> > Is it safe to add –d unwritten=0 option to increase performance like
> this
> > (or will I lose some essential functionality)?:
> >
>
> My understanding (although I'm not familiar with that code),
> is that unwritten extents are used in space preallocation.
> So unless you reserve space for a file it will not have an effect.
> And if you do, then setting "unwritten=0" will speed up writes because it
> doesn't
> need to flag the unwritten extents and write out the extra transactions
> for this.
> If the unwritten extents aren't flagged as such then there can be a
> security issue
> where one can read old data (other's data) for these unwritten parts.
> In fact, the security issue on preallocation (1997-98 sgi-pv#705217) was
> what motivated
> the idea of flagging extents as unwritten in the first place.
>
Thanks for clearing that out :)
> --Tim
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