VPLEX: LUN Z explained

LUNZ is associated to various issues including hosts failing to boot, panics, and performance issues.
 After initial set up, LUNZ was left presented to the 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. LUNZ is host operating system independent and can be presented by different EMC arrays including CLARiiON, VNX, and VPLEX.

As placeholder for connectivity, the LUNZ should be removed from the host following configuration. If the LUNZ remains visible to the host, various issues can occur from a host failing to boot and panicking to performance issues.

There are two primary reasons that a host would see a LUNZ.

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

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

1. Register the host initiators on the array
2. Assign storage to the host initiators in the storage group or storage view
3. Ensure that there is an HLU 0 in the storage group or storage view

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 behavior of LUNZ being presented.
From VPLEX you can change the LUN ID of existing virtual-volume to "0". This volume must be in the storage-view that the Host seeing the LUNZ is accessing. You could also present a small LUN to the VPLEX, build a virtual-volume on top of it, and give the volume a LUN ID of "0" when the virtual-volume is placed into the storage-view.
From ESXi 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 want to reconfigure your storage view to present the volume at 0.


 
When a VMware host sees a LUN Z, and the host is subsequently attached to a storage 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 ESXi 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

Why does my Broadcom (VMware) host have both Host LUN 0 and LUN Z?