Some backup solutions, such as those leveraging VMware Consolidated Backup, can make backups of the contents of SAN LUNs using a physical Windows proxy server. The SAN LUNs are presented to the Windows proxy server in the same manner they are presented to the ESX/ESXi hosts, and the backup software reads data from the LUNs.

If a physical Windows server mounts and writes to existing filesystems on SAN LUNs used by virtual machines, data corruption can occur. It is imperative that the Windows server be configured to not mount filesystems on the SAN LUNs.

This article summarizes information from the Configuring Windows on the VCB Proxy section of the VMware Virtual Machine Backup Guide for ESX/ESXi 3.5-4.0.

All versions of Windows Server OS, except Windows Server 2003 Enterprise Edition and Windows Server 2003 Datacenter Edition, assign drive letters to each visible NTFS and FAT volume. To be able to use Consolidated Backup or similar backup strategies, you need to clear any unused drive letter assignments and then ensure that the backup destinations are visible.

Disable assignment of drive letters

1. Shut down the Windows proxy server.
2. Disconnect the Windows proxy server from the SAN, or mask all LUNs containing VMFS volumes or RDMs. For more information, contact your storage array vendor.
3. Boot the Windows proxy server.
4. Log on as the administrator or as a member of the Administrators group.
5. Open a command-line interface. For more information, see Opening a command or shell prompt (1003892).
6. Run DiskPart with this command:
   
   diskpart
   
   
7. Determine whether automount is enabled with this command:
   
   automount
   
   Example: You might see this output:
   
   Automatic mounting of new volumes enabled.
   
   
8. Disable automatic drive-letter assignment to new volumes with this command:
   
   automount disable
   
   
9. Clear out any entries of previously mounted volumes in the Windows registry with this command:
   
   automount scrub
   
   
10. Exit the DiskPart utility with this command:
    
    exit
    
    
11. Shut down Windows.
12. Reconnect the Windows proxy server to the SAN, or unmask all previously masked LUNs containing VMFS volumes or RDMs. For more information, contact your storage array vendor.
    
    Note: The same host/LUN group, configuration, and LUN presentation should be used for the Windows proxy server as is being used for the ESX hosts. Do not alter this configuration to use a Windows-specific configuration as this may cause failures when attempting to access the LUNs.
    

Validating device visibility on the Windows proxy server

VMFS LUNs appear in Windows Disk Management as Healthy, but are marked as Unknown Partition and are not assigned drive letters. Backup software, such as VMware Consolidated Backup, accesses the storage device directly when performing backups, not through a drive letter. To ensure that the devices are visible:

1. Log on as the administrator or as a member of the Administrators group.
2. Open the Computer Management MMC. Right-click My Computer and click Manage.
3. In the left console tree, click Disk Management.
4. Click the Action menu, and select Rescan Disks.
5. The shared storage devices presented now appear in the list of devices.