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Re: [Xen-users] shrink or grow disk image?

To: Jonathan Ervine <JErvine@xxxxxxxxxx>
Subject: Re: [Xen-users] shrink or grow disk image?
From: John Haxby <john.haxby@xxxxxxxxxx>
Date: Wed, 30 Apr 2008 12:06:33 +0100
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John Haxby wrote:
Of course, if your original file is sparse then shrinking isn't going to actually free disk space but as you've just copied it (using, presumably, cp) then you've filled all the holes with zeroes. If you copy the file with tar and the --sparse options then the holes won't get filled in and you won't be using space that you don't need. I suspect, though I haven't tried it, that copying a file with lots of zero-filled blocks using tar --sparse will convert those blocks into holes. Does that help?

On Fedora 8, at least, cp handles sparse files quite nicely and "cp --sparse=always" seems to do a good job of turning blocks of zeros into holes.

You learn something new every day.


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