If a LUN runs out of space and the containing volume cannot automatically grow more space, 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.
The LUN must be taken offline so that the SCSI inquiry data on both nodes in the HA pair is updated and the host is forced to rediscover the SCSI thin provisioning attributes. The host must release the LUN when it is taken offline and rediscover it after space_alloc has been enabled.