Storage LUNs that are already in use as an RDM appear available in the Add Storage Window

Products

VMware vSphere ESXi

Issue/Introduction

You see LUN IDs that are already in use by a virtual machine as an RDM disk when attempting one of these actions:

Adding a Raw Device Mapping (RDM) to a virtual machine
Adding a new VMFS datastore
Creating a new VMFS datastore

Warning: Data can be overwritten if the LUN is mounted to a virtual machine and written to.

Environment

VMware vSphere ESXi 6.x
VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

Cause

This issue occurs due to inconsistency of the LUN VML ID. The NAA IDs are consistent across all of the ESXi hosts in the environment, but the VML IDs assigned to LUNs are not consistent.

The VML ID mismatch is mostly caused by a storage presentation configuration issue, where one ESXi host is given LUN ID A and another ESXi host in the cluster is given LUN ID B. For example:

NAA ID on Host 1 and Host 2 is consistent:

naa.6005#####################0000
VML ID on Host 1:

vml.02001100006005#####################0000485356333030
VML ID on Host 2:

vml.02000b00006005#####################0000485356333630

Breaking apart the VML ID for a closer understanding: The first four digits are VMware specific, the next two digits are the LUN identifier in hexadecimal.

In the preceding example, on Host 1 the LUN is mapped to LUN ID 17 (hex 11) and on Host 2 the LUN is mapped to LUN ID 11 (hex 0b).

To fetch the VML IDs of the LUN in question, run this command on both of the ESXi hosts:

esxcfg-scsidevs -l -d

For example:

esxcfg-scsidevs -l -d naa.6005#####################0000

naa.6005#####################0000
Device Type: Direct-Access
Size: 40960 MB
Display Name: DGC Fibre Channel Disk (naa.6005#####################0000)
Multipath Plugin: NMP
Console Device: /vmfs/devices/disks/naa.6005#####################0000
Devfs Path: /vmfs/devices/disks/naa.6005#####################0000
Vendor: DGC Model: VRAID Revis: 0123
SCSI Level: 6 Is Pseudo: false Status: degraded
Is RDM Capable: true Is Removable: false
Is Local: false Is SSD: false
Other Names:
vml.02001100006005#####################0000485356333030
VAAI Status: supported

For more information, see Identifying disks when working with VMware ESXi/ESX (1014953).

Resolution

This is not a VMware issue. The issue occurs due to a storage presentation error.

To resolve the issue, ensure the VML IDs for connected LUNs are consistent across all hosts in the cluster.

Note: Ensure to power off any virtual machine accessing the problematic LUN and temporarily bring the LUN offline before proceeding with the steps.

To correct the VML ID inconsistency:

Shut down the virtual machine in which the RDM disk is incorrectly appearing.
Remove the RDM(s) from the virtual machine.
Power off any other virtual machine that may be accessing this LUN.
Unpresent the LUN(s) from the affected ESXi/ESX host(s). For instructions, see How to detach a LUN device from ESXi hosts (2004605)
Perform a rescan of the storage on an ESXi/ESX host. For more information, see Performing a rescan of the storage on an ESX/ESXi host (1003988).
Re-present the LUN(s) to the ESXi host(s).
Perform a rescan of the storage on the ESXi host(s).
Re-attach the RDM disk(s) to the virtual machine.

For more information on VML IDs, see Virtual Disk 'X' is a mapped direct access LUN that is not accessible (1016210). Also, see the Setting LUN Allocations section "For LUNs that are shared among multiple hosts, make sure that LUN IDs are consistent across all hosts" of the vSphere Storage Guide.

Additional Information

For information on identifying disks, VML IDs and NAA IDs, see Identifying disks when working with VMware ESX/ESXi (1014953). Also, see: