XtremIO: LUNZ explained

           

   Article Number:     496817                                   Article Version: 7     Article Type:    Break Fix 
   

 


Product:

 

XtremIO HW Gen1,XtremIO HW Gen2 400GB,XtremIO HW Gen2 400GB Encrypt Capbl,XtremIO HW Gen2 400GB Encrypt Disable,XtremIO HW Gen2 400GB Exp Encrypt Disable,XtremIO HW Gen2 400GB Expandable,XtremIO HW Gen2 800GB Encrypt Capbl

 

Issue:

 

 

LUNZ is associated to a variety of issues including hosts failing to boot, panics, and performance issues.   
     After initial set up, LUNZ was left presented to the host.
                                                           

 

 

Cause:

 

 

LUNZ refers to a fake logical unit zero presented to the host to provide a path for host software to send configuration commands to the array when no physical logical unit zero is available to the host. LUNZ is host operating system independent and can be presented by different EMC arrays including CLARiiON, VNX, VPLEX, and XtremIO.   
   
    As placeholder for connectivity, the LUNZ should be removed from the host following configuration. If the LUNZ remains visible to the host, a variety of issues can occur from a host failing to boot and panics, to performance issues.   
   
    There are two primary reasons a host would see a LUNZ.   

         
  1.         The host HBA is connected to the array, but is not in a storage group, storage view or initiator group.     
  2.      
  3.         The host HBA is in a storage group, storage view or initiator group but the group/view does not have an HLU0 assigned.     
  4.    
                                                             

 

 

Resolution:

 

 

The best way to resolve the issue is to ensure host HBA is connected to the array and in a storage/initiator group or view containing a HLU0. Though it is possible to disable this form of communication on some arrays, it is generally not recommended.   
        
    Steps:   

         
  1.         Register the host initiators on the array.     
  2.      
  3.         Assign storage to the host initiators in the storage/initiator group or storage view.     
  4.      
  5.         Ensure there is an HLU 0 in the storage/initiator group or storage view.     
  6.    
                                                             

 

 

Notes:

 

 

HOST   
    LUNZ visibility to host   
    LUNZ refers to a fake logical unit zero presented to the host to provide a path for host software to send configuration commands to the array when no physical logical unit zero is available to the host.   
    On an Invista instance, the LUNZ device is replaced when a valid LUN is assigned to the HLU LUN0 by the virtual frame.   
    LUNZ has been implemented on Invista to make the array visible to the host OS and PowerPath when no LUNs are bound on that array.   
   
    VNX   
    Note: Setting the arraycommpath to 1 (enabled) creates LUNZ devices.   
    A LUNZ device allows the management interface to communicate with the storage system when no LUNs in the storage system are connected to the server.   
   
    VPlex   
    There is no configuration option for LUNZ on VPLEX.   
    With a backend storage array of VNX/Clariion, you can change the arraycommpath setting on the array to change the behaviour of LUNZ being presented.   
    From VPLEX you need to present a real LUN 0 or you can present a dummy LUN 0 for cosmetic reasons.   
    From ESX this is only cosmetic but can be worrying to see dead paths. A dummy LUN 0 from VPLEX is probably the best solution if you do not wish to reconfigure your storage view to present the volume at 0.   
   
    XtremIO:   
    A LUNZ device allows the management interface to communicate with the storage system when no LUNs in the storage system are connected to the server.   
   
        
    When a VMware host sees a LUN Z, and the host is subsequently attached to a storage/initiator group with a real Host  LUN 0, the VMware storage devices must be rescanned TWICE.     
    The first rescan will delete the LUN Z, but it does not add the real Host LUN 0.   
    A second rescan is necessary to put in place the real HLU LUN 0.    
   
    An ESX host reboot will automatically change LUN Z into real Host LUN 0, if present Host LUN 0 was present.   
   
    LUN Z is an initiator property, not a storage group property   
   
    https://support.emc.com/kb/427205    Why does my VMware host have both Host LUN 0 and LUN Z?