If a LUN runs out of space and the containing volume cannot automatically grow more, the LUN goes offline. To keep a LUN online, you should set the LUN option space_alloc to enable.
The LUN option –space_alloc is set to disable by default. If you leave this option set to disable, then the LUN goes offline when the volume runs out of space and is not permitted to grow. If you set this option to enable, Data ONTAP notifies the host that the LUN has run out of space. However, the LUN stays online. The host cannot write to the LUN, but the host can still read the LUN.