23-02-2014 | Remy van Elst
This tutorial shows you how to create and add a disk image to a KVM vm using virsh. 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.
Host running KVM and virsh
Virtual Machine to add disk to
This was tested on a KVM hypervisor host running Ubuntu 12.04 LTS and a Ubuntu 13.10 virtual machine. The KVM hypervisor uses virsh for management.
The example vm is named
example-vm in virsh (domain).
Execute these steps on the KVM hypervisor host.
cd to the folder where you store your disk images:
Create the new disk image:
qemu-img create -f raw example-vm-swap.img 1G
create a new
raw disk image with a size of 1 GB.
Attach the disk to the example virtual machine using virsh:
virsh attach-disk example-vm --source /var/lib/libvirt/images/example-vm-swap.img --target vdb --persistent
virsh to attach the disk image
/var/lib/libvirt/images/example-vm-swap as a
/dev/vdb) disk to the domain (vm)
--persistent 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
Execute these steps in your virtual machine.
Reboot it so that the kernel sees the new disk:
Partition the drive with
cfdisk. For our example we use filesystem type 82 (linux/linux swap):
Format the disk as swap:
Or format it as ext4:
Make the swap active:
Or mount the partition:
mkdir /mnt/new-disk mount /dev/vdb1 /mnt/new-disk
Add to /etc/fstab for reboot persistence:
/dev/vdb1 swap swap defaults 0 0
Or for the ext4 disk:
/dev/vdb1 /mnt/new-disk ext4 defaults 0 0
That's it. You've now created, attached, formatted and mounted a new disk in your VM.