Mounting a volume for VCB backup fails with "Failed to open the disk:..." in the log (4042481)

Date: May 08
Product & Version: All NVBU
OS Version: Windows
Module & Version: All VMware plugins
Application version: All ESX server versions

Symptoms:
When right-clicking and trying to mount a volume from a Windows machine on your VCB proxy this fails and you can not browse the folders.

Reason:
For this operation, VMware invokes the vcbMounter utility of the VCB framework. It is this VMware utility that fails.

There are several potential reasons for this:
a) This usually means that the VCB proxy cannot access the shared storage the virtual machine is located on. Try using the network transport mode in vmware.cfg (documented in chapter 8.3 of the manual). If the machine can be mounted over the network, the problem is with the storage configuration on the VCB Proxy.

b) Not all combinations of VCB framework, storage and ESX Server are supported by VMware. For example, even though you can create a virtual machine on an iSCSI LUN with ESX Server 3.0.1, backup of such LUNs through VCB is only supported with ESX Srver 3.0.2 and higher.

c) The LUN needs to be available to both the ESX Server and the VCB Proxy. Also, the LUN numbers need to match on both - if you use LUN masking/zoning, this might not be the case, leading to the VCB Proxy looking for a LUN where it can't find one. You can check this in Disk Management on your VCB Proxy.

When right-clicking and mounting a volume from a VM through VCB, NetVault will log informational messages about the progress of vcbMounter in the background. In NetVault 8.1, the log messages will be truncated, but in all cases they will start with:
Information 2008/05/29 17:40:10 51 Data Plugin VCBPROXY [2008-05-29 17:40:10.062 'App' 3908 error] No path to device LVID:44f42528-6f56b83d-a9f0-000e0ca0b3b...
Information 2008/05/29 17:40:10 51 Data Plugin VCBPROXY [2008-05-29 17:40:10.062 'BlockList' 3908 error]
Information 2008/05/29 17:40:10 51 Data Plugin VCBPROXY [2008-05-29 17:40:10.140 'vcbMounter' 3908 error] Error: Failed to open the disk: Cannot access a SA...

The following reasons are common:
- "Error: Failed to open the disk: Cannot access a SA..."
The above indicates a problem accessing the LUN locally from the VCB proxy. While the ESX Server sees the virtual machine and presents it for selection, the VCB proxy can't access it. This can usually be resolved by checking the SAN path to the LUN from the VCB Proxy.

If the device is available on the VCB Proxy, double-check the VMware compatibility lists to verify that your combination of access method, VCB framework version and ESX server version is supported.

In order to identify whether SAN access is the problem, try configuring the VMware plugin to use the slower LAN transport mode in vmware.cfg (documented in chapter 8.3 of the manual). vcbMounter will then obtain the mount through the network, which rules out any potential issues on the SAN but is obviously much slower.

- "Error: Backup Snapshot already exists"
A snapshot is still present from a previous (aborted or otherwise failed) backup or mount operation. Refer to solution 3708 - "Backup using the VMware plugin fails and leaves the Virtual Machine image mounted".

- "Cannot open disk file: Error : Unable to open 'blklst://snapshot-1730[datastorename] VirtualMachine/VirtualMachine.vmdk@ESXserver'. Failed to configure disk scsi0:0"
If this is not accompanied by a further error message, it most likely indicates a problem with access rights. In order to resolve this, stop the NetVault service, open the Services on the VCB Proxy (Control Panel -> Administrative Tools) and right-click on the "NetVault Process Manager". Change the "Log On As" for this server from "Local System" to a Domain Administrator account. Restart the service and try browsing again.

In order to determine whether the VMware Plugin plays a role in any issue, you can determine the exact command line used by the plugin for VCBMounter by enabling trace and checking the sysexec file. Try running the command directly from a command prompt. If this also fails, the problem lies with VMware.

German Solution: 4326