Re: [Qemu-devel] disk image: self-organized format or raw file

[Xingbo Wu <wuxb45@gmail.com>]

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On Tue, Aug 12, 2014 at 2:52 PM, Richard W.M. Jones <rjones@redhat.com>
wrote:

> On Tue, Aug 12, 2014 at 07:46:30PM +0100, Daniel P. Berrange wrote:
> > Taking the compression feature - arguably the biggest benefit of that
> > is when you distribute disk images. eg if someone provides a root disk
> > image on a web server, using compression in qcow2 can dramatically
> > lower the download size, while still allowing QEMU to directly run
> > from that qcow2 file. Sure you could wrap your disk images in gzip
> > and then convert to your local filesystem at time of use but this
> > introduces multiple extra steps.
>
> It would be nice if qemu could handle xz-compressed files
> transparently, since (when prepared correctly) these files are
> seekable.
>
> I have written code to do this here:
>
>   https://github.com/libguestfs/nbdkit/tree/master/plugins/xz
>
> I believe it's ideal for read-only backing file, the xz-compressed image
would be very space efficient for distribution :).
Would you consider replace xz with lz4? it has faster decompression speed
(~500MB/s)[1] and client-side decompression would be made painless.

[1]
http://linuxaria.com/article/linux-compressors-comparison-on-centos-6-5-x86-64-lzo-vs-lz4-vs-gzip-vs-bzip2-vs-lzma

> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> libguestfs lets you edit virtual machines.  Supports shell scripting,
> bindings from many languages.  http://libguestfs.org
>



-- 

Cheers!
       吴兴博  Wu, Xingbo <wuxb45@gmail.com>

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