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Re: [Qemu-devel] RFC for new features

From: Julian Seward
Subject: Re: [Qemu-devel] RFC for new features
Date: Fri, 9 Jul 2004 11:34:58 +0100
User-agent: KMail/1.6.2

On Friday 09 July 2004 11:02, Johannes Schindelin wrote:
> Hi,
> On Thu, 8 Jul 2004, Thomas Munn wrote:
> > 1.  Definately a DISK manager/compressor ala vmware disk images (so I
> > don't have to waste 4+gb if I don't have a full fileysystem!)
> Fabrice already mentioned that, right? I would favor using cloop devices,
> i.e. using the toolset from cloop to create compressed "devices". Knoppix
> uses this system to pack much more than 700MB on a CD.
> The advantage of cloop as compared to gzip'ed filesystem: Everytime you
> seek in the file, with gzip you have to either have stored a certain zlib
> state or decompress the whole file up to that point. With cloop this
> problem is solved.

I don't think it's a good idea to compress the real data in the filesystem
it reduces performance and adds complexity.  All that's needed is
to modify the current cow disk system so that unused sectors don't take
any (much) space in the .cow file _without_ having to rely on filesystems
which support holes in files.

vmware (afaik) doesn't really compress disk images, at least not
compression in the gzip/zlib sense.  What it does is understand the
filesystem in the disk image, so it knows where the unused sectors are,
and arranges for them to take more or less zero space in the .vmdk

> The Ctrl-Shift-F2 monitor thing is a cute idea, but I really would like to
> at least optionally retain the old style monitor.

I agree it is a good idea.  Mostly I just want to run WinXP without
having to have a seperate xterm for the monitor, so I vote in favour
of this one.


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