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Date: Mon, 3 Nov 2008 18:12:14 +0100
From: Fabian Keil <freebsd-listen@fabiankeil.de>
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"Marc G. Fournier" <scrappy@hub.org> wrote:

> I have a disk img for qemu that is 4G, but disk usage is only 650M ... du=
e to=20
> how the image is created, it will grow to 4G, but only uses as much as it=
 needs=20
> ... but, if I run a simple 'cp' on the file, it goes from:
>=20
> image: debian.img
> file format: raw
> virtual size: 4.0G (4294967296 bytes)
> disk size: 652M
>=20
> to:
>=20
> image: dtc.img
> file format: raw
> virtual size: 4.0G (4294967296 bytes)
> disk size: 4.0G
>=20
> Is there a way of moving things around such that it *maintains* the holes=
,=20
> instead of fills them in?

Quoting dd(1):

| conv=3Dvalue[,value ...]
|          Where value is one of the symbols from the following list.
[...]
|          sparse   If one or more output blocks would consist solely of
|                   NUL bytes, try to seek the output file by the required
|                   space instead of filling them with NULs, resulting in a
|                   sparse file.

I haven't actually tested it with qemu images, though.

Fabian

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