What is a LUNZ device?

About

LUNZ is defined as :

The logical unit number that an application client uses to communicate with, configure and determine information about an SCSI storage array and the logical units attached to it. The LUN_Z value shall be zero. In the EMC context, 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 EMC array, the LUNZ device is replaced when a valid LUN is assigned to the HLU LUN0 by the Storage Group. The agent then communicates through the storage device. The user will continue, however, to see LUNz in the Device Manager.

LUNz has been implemented on EMC 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).

LUNz should disappear once a LUN zero is bound, or when Storage Group access has been attained.

To turn on the LUNz behavior on EMC arrays, you must configure the arraycommpath flag.

Explanation

LUNZ is a placeholder. It is as simple as that. In HP-UX 11.31, ioscan runs without human intervention. Thus you can end up in a situation where your server can see the storage array, but no LUNs are presented to the server … yet. And thus you get LUNZ. The same applies for 11.23 and below, but it is unlikely that you scan for devices before your storage admin comes along.

You then end up with:

# ioscan -funNC disk
Class     I  H/W Path  Driver S/W State   H/W Type     Description
===================================================================
disk      1  64000/0xfa00/0x8    esdisk   NO_HW       DEVICE       EMC     LUNZ
disk     29  64000/0xfa00/0x4e6  esdisk   CLAIMED     DEVICE       EMC     SYMMETRIX
                      /dev/disk/disk29      /dev/disk/disk29_p2   /dev/rdisk/disk29     /dev/rdisk/disk29_p2
                      /dev/disk/disk29_p1   /dev/disk/disk29_p3   /dev/rdisk/disk29_p1  /dev/rdisk/disk29_p3

You might also see following in the SYSLOG:

Jan  5 12:51:51 serv1 vmunix:
Jan  5 12:51:51 serv1 vmunix: 	device id = loop id, for private loop devices
Jan  5 12:51:51 serv1 vmunix: 	device id = nport ID, for fabric/public-loop devices
Jan  5 12:51:51 serv1 vmunix: 0/0/0/5/0/0/1.0x14: Device at device id 0x651800, PWWN 0x50001442c002c801 has disappeared from
Jan  5 12:51:51 serv1 vmunix: 0/0/0/5/0/0/1.0x14: Device at device id 0x651c00, PWWN 0x50001442c0004f01 has disappeared from
Jan  5 12:51:51 serv1 vmunix: Name Server GPN_FT (FCP type) response, or its 'Port World-Wide Name' has changed.
Jan  5 12:51:51 serv1 vmunix: System won't be able to see LUNs behind this port.

And no matter how many times you do ioscan -fn, you get no devices. Before you go yelling at your storage admin, then try to remove the LUNZ device:

# ioscan -funNC disk | grep LUNZ

   disk      1  64000/0xfa00/0x8    esdisk   NO_HW       DEVICE       EMC     LUNZ

# rmsf -H 64000/0xfa00/0x8

Then check that the LUNZ device is gone:

# ioscan -funNC disk | grep LUNZ | wc -l
0

Try to get the LUNs onboard:

# ioscan -funNC disk

# insf -e

Check. Lo and behold. They are available now:

# ioscan -funNC disk
Class     I  H/W Path  Driver S/W State   H/W Type     Description
===================================================================
disk     29  64000/0xfa00/0x4e6  esdisk   CLAIMED     DEVICE       EMC     SYMMETRIX
                      /dev/disk/disk29      /dev/disk/disk29_p2   /dev/rdisk/disk29     /dev/rdisk/disk29_p2
                      /dev/disk/disk29_p1   /dev/disk/disk29_p3   /dev/rdisk/disk29_p1  /dev/rdisk/disk29_p3
disk      1  64000/0xfa00/0x4fc  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk1   /dev/rdisk/disk1
disk     59  64000/0xfa00/0x4fd  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk59   /dev/rdisk/disk59
disk     60  64000/0xfa00/0x4fe  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk60   /dev/rdisk/disk60
disk     61  64000/0xfa00/0x4ff  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk61   /dev/rdisk/disk61
disk     62  64000/0xfa00/0x500  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk62   /dev/rdisk/disk62
disk     63  64000/0xfa00/0x501  esdisk   CLAIMED     DEVICE       EMC     Invista
                      /dev/disk/disk63   /dev/rdisk/disk63