copying 'holey' files ...
Fabian Keil
freebsd-listen at fabiankeil.de
Mon Nov 3 09:12:22 PST 2008
"Marc G. Fournier" <scrappy at hub.org> wrote:
> I have a disk img for qemu that is 4G, but disk usage is only 650M ... due to
> how the image is created, it will grow to 4G, but only uses as much as it needs
> ... but, if I run a simple 'cp' on the file, it goes from:
>
> image: debian.img
> file format: raw
> virtual size: 4.0G (4294967296 bytes)
> disk size: 652M
>
> to:
>
> image: dtc.img
> file format: raw
> virtual size: 4.0G (4294967296 bytes)
> disk size: 4.0G
>
> Is there a way of moving things around such that it *maintains* the holes,
> instead of fills them in?
Quoting dd(1):
| conv=value[,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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