Resizing my KVM
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[Remember that even though I work for IBM I am an individual with my own thoughts and ideas. Anything I write here may not necessarily represent the views of the IBM Corporation or its partners... though I'm hoping that's only a matter of time before they catch up.]
As most of you know, or at least suspect, I run Linux. It's my lifestyle. However, I have to interact with people who have different lifestyles. This requires a level of tolerance and sometimes even walking in others' shoes. Yes, I sometimes have to do something that is only available to me through Microsoft Windows. The situations are rare. If I'm in on the front end I'm usually able to get people to agree on more standard information formats that are not necessarily tool-bound so I can work behind the scenes. However, when I'm coming into someone else's project or meeting I don't get to influence that at all.
I suppose I do tend to act a little confused that Windows is required for this and say that I'll need to get hold of a Windows machine that I can use. Then I fire up my virtual machine. I used VMWare for a while, but I just get a little nervous about having important functionality wrapped up in a single, closed-source provider, even when it's free. In a previous blog post I talked about how I successfully converted my VMWare image to a kvm image. I still haven't mastered some of the things like getting USB interaction the way I want, but that's less critical to me right now. It's been working great for my needs.
However, I ran into a problem. Working in a big corporate environment we have big corporate security snooping. I don't whine about this. They make computer resources available to me and give me some freedom to manage it myself. (I know some people who have their laptops built for them and are not allowed to do anything with the software.) In exchange for my technical freedoms I think a little compliance verification is reasonable. So, I'm getting nasty grams that my computer is failing tests. I look at things and everything seems fine. Then I realize it could be the seldom-used virtual machine. I fire it up and it does look like it hasn't completed some of its verification. It needs some updates and such. OK. We'll let it do its thing.
DOH! My virtual hard drive is full!
I can't go anywhere with this until I get the updates done. I don't really want to start from scratch. What do I do?
Well, as it turned out, resizing the virtual KVM drive was pretty
easy, and even fun. So, I'm leaving my steps here in case anyone else
needs to do it. I will warn you, that messing around with virtual
images like this often involves making copies of the whole thing, so
you need to have PLENTY of drive space. In my case I have a 2 TB USB
drive for backups and archives where these images live. I had hundreds
of gigs of space available, so this was not a problem. Most of the
information that I got to do this came from the article, "HOWTO:
Resize a KVM Virtual Machine Image" on IT.Signals. It largely
worked, with a few critical differences. Thanks to Etienne for gettting
me pointed in the right direction.
Basically here are the steps that we are going to do:
Preparing the virtual drive
When I created my KVM, I used the qcow2 format. This format
will only allocate the physical drive space that it requires to hold
the filesystem. In other words, if I have a 30GB virtual drive,
but am only using 10GB, then my virtual drive file will be 10GB. I tend
to use this because it makes the base images more
portable. Why push 30GB of bits across the network when you can
do it in 10? However, the technique that we're using to resize
the drive works better if everything is in the raw format. (I
finally figured this out after about three tries. You're welcome.)
If you are already using a raw image, then you can skip this
step. Otherwise you must convert your existing image to raw so we
can append it. Fortunately this conversion is easy and the way
I'm doing it, you automatically get a backup of your original, which
you want to have anyway. We use the kvm-img
This will take a while to do as it copies gigs of data. When
you are done, you will have the original image and a new one in the raw
format. The size may grow as it fills in any compressed space
Create the appended space
This is pretty straight forward. We are going to create a
blank virtual drive. I want to add 20GB to my existing image, so
I use kvm-img
with these options:
This happens relatively quickly, compared to the copy. A 20GB file is created which is essentially a bunch of zeroes.
Combine the files
Now we are going to append this blank space to our raw drive. The original instructions had me export both raw drives into yet another file, but I found I could use the existing file and save some time and space.
Resize the partition
Now comes the truly fun part that makes virtual machines so much
fun. I'm going to use a downloadable, Linux-based tool to boot
this drive image and work with it. Here we're not really doing
much more than if we popped a CD into the drive, but the parameters
we're using can be used to remix a virtual machine on the fly with
multiple drive resources. I'll probably do some experimentation
with this later. For now, we're just going to use it to boot the
CD we want.
The tool we are going to use is called gparted. It
is included with many distributions and is used to let you
manipulate your partitions. As it turns out, the developers of
this tool have created a LiveCD which boots a small version of Linux
and jumps straight into the tool. Very cool! The CD is
available from their download
site. Just get the .iso file. You don't need to burn
the CD (though you'll want this in your kit!). We'll be using the
image to get started.
Let's parse that command:
KVM will now boot from the gparted CD, taking us directly into the tool (after a few language choices and other confirmations). Figure 1 is a screenshot of the tool in action.
Figure 1. resizing a partition with the gparted LiveCD.
The screen shot is not of my actual editing session with the Windows image. (I finished all that before I knew I was going to write this.) Here I am using the same technique with an Ubuntu Studio image, but the mechanics are the same. Use your mouse to select the partition that you want to resize. Then hit the Move/Resize icon in your navigation bar to edit the partition. In my case it was just a single NTFS partition followed by unallocated space. I simply grew the NTFS and it was fine. If working with partitions like this is new to you, you might want to check out the documentation on the gparted web site.
When you have completed this step, you will have successfully changed the size of your KVM image. It is currently in a raw form, which means that it takes up the full amount of disk space that has been allocated to the virtual drives, but that might be OK for your needs.
Compressing the qcow2 image
If you don't want to leave your image in the raw format you can
convert it back to any format you wish. In my case, I started
with a qcow2 image and want to go back. Since the whole point of
using qcow2 is to compress the unused space I want to make sure that I
take that space back when I convert. Again, kvm-img
takes care of my needs.
Again, let's look at these parameters in detail:
This will take a while, but when I'm done I will have a fresh,
resized version of my kvm image. I will also have the original
backup image (.cya) along with the .raw images which can be deleted.
|cat addon.raw addon.raw addon.raw >> MyKVM.img.raw|
I hope this is helpful to someone. If anyone has comments or
suggestion for easier ways to handle this, I'm open. I strongly
recommend checking out some of the various LiveCD tools that are
floating around like gparted. If you want to fire one up you can
use KVM to do it easily, using the same process that we used