[one-users] error when attach disk

[song]

Hello guys:

I am trying to attach disk to a running vm on a CentOS 6.4 node.The
guest OS is redhat 5.7.Libvirt version is 0.9.4,and qemu version is
0.12.1.Attach operation is failed and the log as follows:

Wed Oct 23 17:22:05 2013 [VMM][E]: attach_disk: Command "virsh --connect
qemu:///system attach-device one-81 /cluster1-1/103/81/disk.2.attach"
failed: error: Failed to attach device from /cluster1-1/103/81/disk.2.attach
Wed Oct 23 17:22:05 2013 [VMM][I]: error: operation failed: drive
hotplug is not supported
Wed Oct 23 17:22:05 2013 [VMM][E]: Could not attach
/cluster1-1/103/81/disk.2 (vdb) to one-81

The attach xml as follows:

<disk type='file' device='disk'>
<driver name='qemu' type='qcow2' cache='default'/>
<source file='/cluster1-1/103/81/disk.2'/>
<target dev='hdd'/>
</disk>

Any help is appreciated!