DLoop comments

Phillip Susi psusi at cfl.rr.com
Wed Sep 28 16:24:37 CDT 2005

Matt Zimmerman wrote:
> Which wiki page(s) are you referring to here?

The DLoop wiki.  https://wiki.ubuntu.com/DLoop

  > A block containing all zeroes is perfectly valid data, and the 
system can't
> treat it as a signal to revert to the old, pre-COW data (which itself isn't
> necessarily all zeroes).  Indeed, having the filesystem zero out unused
> blocks would actually increase the number of COW actions, in the natural
> course of modifying and deleting files which are included in the base cloop
> image.

Oops, that is true.  The mapper would have to verify that the original 
was all zeroes.

> Addressing this issue is not as simple as it sounds.  Fortunately, there are
> some alternative technologies available which we are experimenting with to
> increase performance here (including unionfs and squashfs).

Yes, unionfs looks to be by far the best solution, though it seems to be 
in early development.

> I'm not sure that I understand your suggestion correctly, but it does not
> sound at all straightforward to implement.  Certainly the current planned
> solution (installing by copying the preinstalled filesystem) is much simpler
> and more robust.

It seems prety straightforward to me.  The .deb explains where dpkg 
should extract the files to on install.  Rather than copy, dpkg could 
move the file to the target.  Then when you install the package to 
another target, the .deb still contains the path where the file was 
moved to, so it can be retrieved.

Doing a straight copy of the livecd to the target has a few problems:

1) The user might not want to install _everything_ that is on the livecd
2) The user might want to install more updated packages downloaded from 
the network
3) Some differences in configuration may be needed when installed to a 
hard drive than when installed on the livecd

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