[fedora-virt] info on resize support for virtio disk

[Richard W.M. Jones]

On Fri, Apr 29, 2011 at 05:01:42PM +0200, Gianluca Cecchi wrote:
> I extend the disk with qemu-img at host side:
> qemu-img resize /var/lib/libvirt/images/f15_001.img +1G
>
> In guest neither partprobe nor kpartx show any change...
> I put the xml definition in disk.xml and try to update device from
> libvirt point of view (my domain id is 4):
>
> [root ~]# virsh update-device 4 disk.xml
> error: Failed to update device from disk.xml
> error: unsupported configuration: disk bus 'virtio' cannot be updated.

At the qemu level, what has to happen is that the "block_resize"
command gets sent to the human monitor.  It appears from the output
above that libvirt doesn't support that.

However a bigger problem is that guests don't see the resize if any
active (eg. mounted / in use) partition is on the disk, and since
almost any useful disk is going to have multiple active partitions,
this really is a show-stopper.

So basically we don't support this in any useful sense of the word.  I
always say from experience that resizing disks is *much* harder than
people imagine.  I've not seen any guests that can do anything useful
when the disk is (online) resized.

I suggest offline resizing and virt-resize :-)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines.  Boot with a
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