LUNZ or ghost LUN explained briefly.



CLARiiON AX Series, CLARiiON CX Series




CLARiiON Array presents LUNZ (ghost LUN) over iSCSI when no devices are presented.




LUNZ has been implemented on CLARiiON arrays to make arrays visible to the host OS and PowerPath when no LUNs are bound on that array. When using a direct connect configuration and there is no Navisphere Management station to talk directly to the array over IP, the LUNZ can be used as a pathway for Navisphere CLI to send bind commands to the array.  LUNZ also makes arrays visible to the host OS and PowerPath when the host's initiators have not yet 'logged in' to the Storage Group created for the host. Without LUNZ, there would be no device on the host for Navisphere Agent to push the initiator record through to the array. This is mandatory for the host to log in to the Storage Group. Once this initiator push is done, the host will be displayed as an available host to add to the Storage Group in Navisphere Manager (Navisphere Express).


Ghost LUN (LUNZ) is visible on all Linux hosts that are logged in to the AX150i over iSCSI. In summary, this occurs because the arraycommpath setting of 1 creates a virtual LUN 0 for communication with the storage system.


A way of getting rid of LUNZ is to set arraycommpath to a value of 0. The arraycommpath option enables or disables a communication path from the server to the storage system.


This does not work on AX-series arrays. AX150 arrays are shipped with the failover/arraycommpath mode configured as 1 by default. It is not possible to change the failover mode using Navisphere Express or Navisphere Manager. Also, it is not possible to configure the failover mode and arraycommpath setting using CLI.


For CLARiiON AX-series you would need to use storagegroup command:


storagegroup sethost -arraycommpath


Note: Do not issue the storagegroup command unless you know the appropriate value for the type of failover software running on the attached servers. The command is designed for transition from one type of failover software to another. Changing the arraycommpath mode to the wrong value will make the storage system inaccessible.



Refer to Primus Solution ID “emc170849” for more information on the issue.