Disabling Automount on Backup Servers

Many hypervisor-based backups perform a “HotAdd” type of backup. A HotAdd backup takes a snapshot of a VM, mounts the VM drives on the backup host, and backs it up as if it were a local disk. This has significant advantages as it achieves speeds akin to a SAN backup.
Now the bad news. If your backup server (Backup Proxy, Media Agent, etc.) is a Windows Server, you’ll have an additional wrinkle to deal with, which is that Windows will try to automount the newly-added drive to the OS, assign a drive letter to it, and prepare it for file access. Furthermore, in some cases, if someone is logged into the server when a drive is automounted, Windows may ask the user to format the drive! CAUTION: at this point we may be one mis-click away from disaster!

Thankfully, we have a very simple fix for this situation. On your backup server, fire-up an admin command prompt, and enter the following:

diskpart
automount disable
automount scrub
exit

That’s it! Here’s how it works. Diskpart is a Windows Utility used to manage disks in your system. As simple as this solution seems, please be cautious with your use of diskpart. It offers the same functionality as the Disk Management plug-in, but includes a few more commands and features than the GUI provides.
Diskpart starts the utility and puts you at a DISKPART> prompt. This informs you that you are in diskpart and not in a standard Windows or Powershell prompt.
“Automount disable” will tell the system you no longer want it to mount newly-presented disks and assign a drive letter.

“Automount scrub” is the housecleaning command. It takes the drive letters, mounted folder paths, mounted folder directories, and registry settings the host no longer sees, and scrubs them from the host. That way, if the drive is re-presented (say, in the next backup cycle) it won’t remember the drive and try to remount it.

“Exit,” well, exits diskpart.

Now, whenever you run backups, the backup server will not try to mount the VM disks when they are presented to the server. Run with your backup server with confidence, knowing your image level backups are used to backup only the VMs!