sparse files

[Matthew Carpenter]

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Roger Oberholtzer wrote:

>(I deleted Matt's question about why I don't just gzip things. Here is
>a reply.)
>
>When I make a sparse image for use with qemu, say 6GB, very little is
>actually allocated from my hard disk. It only really takes space when I
>really put something in the file. With qemu, I use this file as a 'disk
>image' into which an operating system can be installed. As such, it must
>have some concept of size (in my case 6GB). Effectively, I am telling
>qemu that there is a partition that is 6GB. In this image, the operating
>system can do whatever it likes, just as it would with a partition. But
>the space taken on my hard disk is only what the installed operating
>system actually puts there. Not the full 6GB.
>
>Of course, I could tell qemu to use a file where storage from the hard
>disk has in fact been taken. Then gzip or is an option for transporting
>these images.
>
>If I install w98 into a 6 GB sparse file, it will only really take 300M
>or so. So, I could back up the 6 GB image to a CD. It the file is really
>6GB, it will take more. OK, I would initialize the space to 0, so if it
>is not used the compression may be quite good.
>
>What I am wondering (another experiment) is if I remove content from a
>sparse file, does the space allocated for it decrease as well?
>
>Disk space is cheap these days. But sparse files seem less wasteful.
>
Thanks Roger.
I was under the impression this "sparse technology" was a part of
qemu, but you're talking about the OS-related Sparse file, which has
nothing to do with qemu at all.  Correct?

Sorry for the misunderstanding.  My experience with sparse files is
nil at this point.

- --
Matthew Carpenter
matt at eisgr.com                          http://www.eisgr.com/

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