====== Ubuntu - KVM - Add Disk Image ======

This is useful when you for example want to expand the disk space of your virtual machine when it is using LVM, or if you want to add a swap disk to a virtual machine.

Note that you can also create a swap file instead of a disk, however, this is an example for adding the disk.

===== Requirements =====

  * Host running KVM and virsh
  * Virtual Machine to add disk to

The example VM is named **example-vm** in virsh (domain).

----

===== Create and attach the disk image =====

Execute these steps on the KVM hypervisor host.

cd to the folder where you store your disk images:

<code bash>
cd /var/lib/libvirt/images/
</code>

----

===== Create the new disk image =====

<code bash>
sudo qemu-img create -f raw example-vm-swap.img 1G
</code>

We use **qemu-img** to **create** a new **raw** disk image with a size of 1 GB.

----

===== Attach the disk to the example virtual machine using virsh =====

<code bash>
virsh attach-disk example-vm --source /var/lib/libvirt/images/example-vm-swap.img --target vdb --persistent
</code>

We use virsh to attach the disk image **/var/lib/libvirt/images/example-vm-swap** as a **virtio** (**/dev/vdb**) disk to the domain (vm) **example-vm**.

The **--<nowiki>persistent</nowiki>** option updates the domain xml file with an element for the newly attached disk.

Note that if you already have a **/dev/vdb** disk you need to change **vdb** to a free device like **vdc** or **vdd**.

----

===== Reboot the Virtual Machine =====

Reboot so that the kernel sees the new disk.

Execute this in the virtual machine.

<code bash>
sudo reboot
</code>

----

===== Partition the drive =====

Partition the drive with **cfdisk**.

For our example we use filesystem type 82 (linux/linux swap):

Execute this in the virtual machine.

<code bash>
cfdisk /dev/vdb
</code>

Format the disk as swap:

<code bash>
mkswap /dev/vdb1
</code>

or format it as ext4:

<code bash>
mkfs.ext4 /dev/vdb1
</code>

----

===== Make the swap active =====

<code bash>
swapon /dev/vdb1
</code>

or mount the partition:

<code bash>
mkdir /mnt/new-disk
mount /dev/vdb1 /mnt/new-disk
</code>

----

===== Make the new disk persistant =====

Add to /etc/fstab for reboot persistence:

<file bash /etc/fstab>
/dev/vdb1   swap            swap    defaults    0 0
</file>

or for the ext4 disk:

<file bash /etc/fstab>
/dev/vdb1   /mnt/new-disk   ext4    defaults    0 0
</file>

That's it.  You've now created, attached, formatted and mounted a new disk in your VM.

----

===== References =====

  * qemu-img man page [http://linux.die.net/man/1/qemu-img]
  * virsh-attach doc page [http://builder.virt-tools.org/artifacts/libvirt-virshcmdref/html/sect-attach-disk.html]