KVMdiskAttachOnline

1) create appropriate underlying device

2) create xml file containing libvirt disk definition regards existing domain xml (target dev etc.)

<disk type="block" device="disk">
          <source dev="/dev/R1_SSD/dsd_e"/>
          <target dev="sdc" bus="virtio"/>
          <driver name="qemu" cache="writethrough"/>
       </disk>

3) attach disk to desired domain like this:

virsh # attach-device servername /etc/libvirt/cluster/lazne/qemu/dsd-disk.xml

4) Don't forget to add this disk xml snippet to domain xml file.