Error Code 91:30 Unable to open the disk(s) for Virtual Machine.

Article ID: VMW0004 Virtual Server Agent (VSA) intermittently failing in hotadd mode to open disk for backup.


Backup job fails with error

Error Code 91:30 - Unable to open the disk(s) for Virtual Machine [VM]. Please ensure that the proxy is able to communicate with the ESX host and resolve the ESX host address. Also verify that the disks types configured to the virtual machine are supported.

From the VixDiskLib.log you will see log entries similar to the following:

### W32Util_DismountVolumes: FSTCL_LOCK_VOLUME failed on volume \\?\Volume{37d4197c-6f51-11e1-953e-005056900048}: 5
### W32Util_CloseDismountHandle: Unlocking and closing handles for 1 volumes on PhysicalDrive1...
### DISKLIB-FLAT : Open: Failed to dismount physical drive 1. Perhaps its volumes have open files on them?
### DISKLIB-FLAT : "\\.\PhysicalDrive1" : failed to open (73): .
### DISKLIB-LINK : "C:\Windows\TEMP\vmware-SYSTEM\4210cc8e-55ae-f4eb-e1a3-53392e9bd7f1-vm-383\hotadd\VmdkStubs\" : failed to open (The physical disk is already in use).
### DISKLIB-CHAIN : "C:\Windows\TEMP\vmware-SYSTEM\4210cc8e-55ae-f4eb-e1a3-53392e9bd7f1-vm-383\hotadd\VmdkStubs\scsi0-0-0-vm.vmdk" : failed to open (The physical disk is already in use).
### DISKLIB-LIB : Failed to open 'C:\Windows\TEMP\vmware-SYSTEM\4210cc8e-55ae-f4eb-e1a3-53392e9bd7f1-vm-383\hotadd\VmdkStubs\scsi0-0-0-vm.vmdk' with flags 0x1e The physical disk is already in use (73).


And from the vsbkp.log you may see log entries similar to the following:

CVMWareInfo::_MountVM_VCB4() - Opening Disk [[DS] VM/VM.vmdk] as [DS] VM/VM [.vmdk]
CVMDiskInfo::OpenHostDiskHandle() - Opening disk [.vmdk] on VM [VM] path [[DS] VM/VM.vmdk] flags [ Readonly ]
CVMDiskInfo::Dispatch_VixDiskLib_Open() - VixDiskLib_Open failed Err=d You do not have access rights to this file
CVMDiskInfo::CloseHostDiskhandlesOnFailure() - There are no handles to close.
CVMDiskInfo::OpenHostDiskHandle() - Failed to open disk handle for [[DS] VM/VM .vmdk]
CVMDiskInfo::OpenDisk() - Failed to open disk handle for [[DS] VM/VM.vmdk] disk from [ ] host


LUNs have been previously mounted on the proxy host. Windows will mount and assign drive letters for previously mounted/known LUNS even if automount is set to disabled.  The state of automount only affects new/unknown LUNS

VMware LUNs mounted for backup are not assigned drive letters. The Virtual Server Agent software accesses the LUNs directly when performing backups.


On the proxy host at an Administrator level command (cmd.exe) prompt, enter diskpart to start Microsoft's disk partitioning utility.  Run the following DISKPART commands

DISKPART> automount disable

DISKPART> automount scrub


The "automount disable" command stops Windows from trying to write signatures to new disks by presenting LUNS in read only mode (SAN backup/LAN restore). The "automount scrub" command clears out previously mounted volumes from the windows registry. 

If disabling automount is not possible due to other functions performed by the proxy host, you can avoid automounting issues by using IntelliSnap to perform a snap backup of the VM volumes and then copy the data (backup copy) from the snap to protected storage.

For more information on the VMware automount issue see