SMSQL verify with greater than 2TB VMware RDM LUN

CJSCOLTRINITY — Thu, 05 Jun 2025 05:51:21 GMT

I have a SQL Server with a 3TB LUN. This is running as a VMware virtual machnine under vSphere 5.1. It was configured with the Microsoft iSCSI initiator within the VM and the LUNs mapped to this initiator. I have now changed the VM so that it uses RDMs with the LUNs mapped to the vSphere cluster of ESXi hosts. I have done this with other SQL servers and they are working fine. The issue I have is that when I run a full database backup with a verify it fails to attach the LUN clone of the 3TB LUN from the snapshot to the VM as a RDM. In the vCenter logs I can see that the tasks fails with the message

Incompatible device backing specified for device '0'.

In the SMSQL log I see

SnapDrive Error]: Failed to create disk in virtual machine, Failed to Map virtual disk: Incompatible device backing specified for device '0'..

(SnapDrive Error Code: 0xc00403e3)

[21:48:35.279] [SnapDrive Error]: Failed to create disk in virtual machine, Failed to Map virtual disk: Incompatible device backing specified for device '0'..

I can the same issue if I select the LUN from the snapshot using SnapDrive and attempt to connect it. However I can manually create a LUN clone, map it to the vSphere cluster, rescan for new storage devices on the ESXi host the VM is running on and then manually add the 3TB LUN to the VM as a RDM.

I am running SnapDrive 6.5 and SMSQL 5.2

Anyone else experienced this isue and have a solution for it? I think the issue is on the ESXi side as I found this on the VMware forums but no resolution!

"I am trying to create a RDM disk using vSphere API on VMFS 5 DS wih physical compatibility Mode. Less than and equal to 2 TB RDM lun creation is working fine. My code is working fine with ESX 5.0 and it is creating greater than 2 TB lun. Is anything changed in ESX 5.0u1 and ESX 5.1 for the creation of RDM disk greater than 2 TB as it fails with these versions?

Note: Manual RDM lun creation is working fine.

Reconfigure VM task is failing with below Error:

fault type:VimApi.InvalidDeviceBacking

Description: Incompatible device backing specified for device '0'."

Re: SMSQL verify with greater than 2TB VMware RDM LUN

CJSCOLTRINITY — Wed, 06 Nov 2013 17:01:06 GMT

This is an issue with vSphere 5.1 which will be addressed in 5.1 update 2. I am also told that it is fixed in vSphere 5.5 and will be fixed in 5.0 update 3 (I think it was introduced in 5.0 update 1).

It is documented in the SnapDrive for Windows 6.5 Release Notes that a LUN greater than 2TB cannot be added to a VM as a RDM if using the vCenter credentials, i.e.

"You cannot create an RDM LUN when SnapDrive is configured with vCenter credentials

Message

Incompatible device backing specified for device 0

Description

You cannot create a raw device mapping (RDM) LUN larger than 2 TB on VMFS V 5 DataStore when SnapDrive is configured with vCenter credentials.

Corrective action

There is no corrective action for this issue.

Note:

You can create an RDM LUN greater than 2 TB on VMFS V 5 DataStore if SnapDrive is registered with ESX credentials instead of vCenter credentials."

As detailed in the SDW release notes if you use the ESXi credentials instead of the vCenter credentials then you can add a LUN greater than 2TB, I have tested this. Although that is not a very good solution if you have a cluster of ESXi hosts and the VM can move between them.

It is also detailed in bug 656135. http://support.netapp.com/NOW/cgi-bin/bol?Type=Detail&Display=656135

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SMSQL verify with greater than 2TB VMware RDM LUN

Re: SMSQL verify with greater than 2TB VMware RDM LUN