Re: [Qemu-devel] Wipe patch

[andrzej zaborowski]

On 02/08/06, Brad Campbell <address@hidden> wrote:
> ZIGLIO, Frediano, VF-IT wrote:
> > Hi,
> >   well, this is not a definitive patch but it works. The aim is to be
> > able to wipe the disk without allocating entire space. When you wipe a
> > disk the program fill disk with zero bytes so disk image increase to
> > allocate all space. This just patch detect null byte writes and do not
> > write all zero byte clusters.
> >
>
> I've been giving this some pretty heavy testing over the last week and can say 
> I've not noticed any
> negative performance impact or any other adverse side effects, not to mention 
> the speedup when doing
> re-packing (which I do fairly regularly on both ext3 and ntfs guest 
> filesystems).
>
> While I'm here does anyone know of a simple program, either dos or linux based 
> for wiping unused
> space on fat filesystems? The only ones I've found so far have been windows 
> based.

I don't know if you mean just zeroing unused parts or reordering the
data and stuff like defragmentation. If you mean the former, there's a
universal method:
 dd if=/dev/zero of=xxx; rm xxx
where xxx is a path to a new file on the filesystem, which must be
mounted. It will creata a zero filled file there, which will fill all
availiable space, and remove the file afterwards. I used this when I
needed to send filesystem images through internet so that they
compressed well.
If you add dd=<a-big-number-here> it might take less time to write the file.

> This patch now conflicts pretty heavily with the new AIO changes it would seem. 
> Further
> investigation required.
>
> Ta,
> Brad
> --
> "Human beings, who are almost unique in having the ability
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>
>
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Regards,
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