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KVM allocates entire storage on virtual disk

Posted on 2010-09-17
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Last Modified: 2013-11-15
Hi, I create a virtual machine originally though PXE, and for some reason the virtual disk size becomes the full size. That is, when I do a df inside the virtual machine it shows only 1.2gb used; however, on the host machine it shows the file size as 8gb. Why is that? How do I force the size of the image on the host machine to be the size actually used on the guest

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Question by:BrianGEFF719
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Assisted Solution

by:torimar
torimar earned 2000 total points
ID: 33705836
Could it be the virtual disk was created as "dynamically expanding"?
In that case, the complete maximum size of space may be reserved on the host, but the actual size that the guest uses and sees is only as much disk space as is actually claimed by the virtual machine. In time, this will grow up to the maximum 8 GB.

I'm not sure about KVM, but other virtualization technologies offer this dynamical storage option.
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BrianGEFF719 earned 0 total points
ID: 33705998
So, I resolved the problem. As it turns out I was using a raw image format instead of a "copy on write," or QCOW as it's called in KVM. So that forced the fulled allocation. Creating a new image as qcow2 now only uses on the host exactly what the VM is using.
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by:torimar
ID: 33706216
Congratulations.

However, there is no reason to delete a question just because it has been solved. This is even counter-productive to the idea of an EE solution database. Just select your own answer as the solution, and request a closure.

Also, QCOW is kind of a "disk space on demand" technique, which is not unrelated to the concept of dynamically allocated storage. Can you exclude that it may have been my comment which pointed you to right direction for solving the issue? If you can't, it would only be fair (and standard procedure on EE) to grant me some assist points.
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by:BrianGEFF719
ID: 33706791
Request my own comment.
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