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initall
Asked: 2011-03-08 07:42:20 +0800 CST

KVM and libvirt: How to configure a new disc device to an existing VM?

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I've got an Ubuntu 9.04 server running two VM's. In /etc/libvirt/qemu/machine1.xml two disk devices are defined like this:

<devices>
 <emulator>/usr/bin/kvm</emulator>
 <disk type='file' device='disk'>
   <source file='/vserver/machine1/disk0.qcow2'/>
   <target dev='hda' bus='ide'/>
 </disk>
 <disk type='file' device='disk'>
   <source file='/vserver/machine1/disk1.qcow2'/>
   <target dev='hdb' bus='ide'/>
 </disk>

I need more storage space in at least one of the devices and thought about adding a third hdc device by simply adding one with same style as above and re-organising my mount structure (The virtual sizes of the current qcow2 files are unfortunately limited.)

My problem is that reloading libvirtd and restarting the VM do not result in a new visible device (checked with fdisk).

I'm aware of extending an existing qcow2 file (converting to raw format, cat-ing/adding the new one, using smth. like gparted) - but only as a last resort.

Hopefully it's something very simple I'm missing?

ubuntu-9.04 kvm-virtualization libvirt

1 Answers

  1. Best Answer

    Log in to the VM and shut it down.

    Create a new virtual disk.

    qemu-img create -f qcow2 /vserver/machine1/disk2.qcow2 $SIZE

    Force shut down the VM.

    virsh destroy machine1

    Open the VM configuration in your default editor.

    virsh edit machine1

    Add a new disk stanza like below.

    <disk type='file' device='disk'>
    <source file='/vserver/machine1/disk2.qcow2'/>
    <target dev='hdc' bus='ide'/>
</disk>

    Close your editor. libvirt will automatically reload the configuration.

    Start the VM.

    virsh start machine1
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