Running a Virtual Machine Using Live Mount

The Live Mount wizard enables you to run a virtual machine directly from a stored backup for that VM.

About This Task

You can use this feature to validate that backups are usable for a disaster recovery scenario, to validate the content on the backup, or to access data from the virtual machine directly instead of restoring guest files. 

Virtual machines that are live mounted are intended for short term usage and should not be used for production; changes to live mounted VMs or their data are not retained when the virtual machine expires. The VM expiration period is set through a VM Lifecycle Management policy.

The Live Mount feature uses a 3dfs cache on the MediaAgent that performs the Live Mount. By default, the 3dfs cache is located in the Job Results folder for the MediaAgent; but you can change the path using the s3dfsRootDir additional setting. The 3dfs cache is circular; unused data are pruned from the cache as needed. By default 5% free space is maintained on the cache; but you can change the required percentage of free space using the n3dfsCacheMinFree additional setting.

For each live mount job, the 3dfs cache requires minimum free space equal to the larger of the following values:

  • 20 GB
  • 15% of the total VM size (the sum of the sizes of all VMDKs for the VM) plus the expected writes to VMDKs during the live mount operation

Note: For faster recovery times, the 3dfs cache should be hosted on a solid state drive (SSD) using flash memory storage.


  • Live Mount is only supported from streaming backups and SnapProtect backup copies.
  • A MediaAgent can perform up to five Live Mount operations at a time.

Before You Begin

  • To verify the version of VMware software that is required to support this feature, see System Requirements
  • Perform a Refresh Datacenters operation on the VMware instance:

    Under Client Computers > virtualization_client > Virtual Server, right-click VMware, point to All Tasks, and then click Refresh Datacenters. In the Refresh Datacenters dialog box, the Refresh VM Status and Discover VMs check boxes are not required for Live Mount; ensure that those check boxes are cleared and click OK.

  • Define a Live Mount provisioning policy to limit the impact that live mount operations can have on the operating environment. See Creating a Provisioning Policy for Live Mount.
  • The virtual machine owner or the user group associated with the VM owner (client computer) must have a role assigned that includes Browse and Live Browse permissions. See User Administration and Security - Getting Started.
  • The vCenter user account must have permissions set as described in Permissions for Custom User Accounts, including Virtual Machine > Interaction > Device connection as well as all permissions for streaming backups and restores.
  • If a firewall is used, provide settings as described in Entering Required Firewall Settings.


  1. In the CommCell Console, display virtual machines under Client Computers as described in Show Virtual Machines in Client Computers List.
  2. Navigate to Client Computers.
  3. Right-click the virtual machine and select All Tasks > Live Mount.

    The Live Mount wizard launches.

  4. On the Select Recovery Points page:
    1. Select one of the following:
      • Mount VM from the latest backup and configuration: Use the most recent backup and configuration data to mount the virtual machine.
      • Select Point in Time: Select date and time values to indicate the backup for which the live mount should be performed.
    2. Copy Precedence (SnapProtect only): To restore from a backup copy, enter the number of the storage policy copy associated with the backup copy. If you leave the default value of 0, the copy with the highest precedence number is used.
    3. Click Next.
  5. In the Virtual Machine Location page:
    1. VM Lifecycle Policies: Select the live mount provisioning policy to be used.
    2. VM Name: The name of the virtual machine is used automatically, with 'VM' appended at the end of the name to distinguish the live mounted VM from the original VM. If you change the name, use a name that is unique on the destination vCenter.
    3. Select a network connection for the VM:
      • No Network: Mount the VM without a network connection.
      • Original Network: (Not recommended) The live mounted VM has the same configuration as the original VM and might conflict with it if they are both on the same network.  If you select this option, you must confirm that you want to proceed with this option.
      • Select Network: Choose an available network from the list (as configured in the provisioning policy). 
  6. In the Submit Job/Alert page:
    1. Select one of the following Job Initiation options:
      • Immediate: Run the job immediately when the live mount request is submitted.
      • Schedule: Next to Configure Schedule Pattern, click Configure to enter a schedule pattern for running the live mount job on a regular basis.
    2. Under Configure Alert, click Add Alert to add an alert for the live mount job.
    3. Click Finish to submit the live mount job.


When a live mount is initiated, an ESX server is selected to host the virtual machine, based on the criteria set in the live mount provisioning policy. The backup is exposed to the ESX server as a temporary datastore. The configuration file for the live mounted VM is updated to reflect the name of the new VM, disks are redirected to the datastore, and network connections are cleared and reconfigured to the network selected for the live mounted VM. When this reconfiguration is complete, the VM is powered on. The virtual machine can be launched from vCenter or the Web Console.

Note: The live mount expires automatically based on the decommission setting in the live mount policy, resulting in cleanup of the snapshot on the ESX server. You cannot manually unmount the VM from the CommCell Console or vCenter; but you can remove the live mounted VM by using the Web Console to power down and delete the VM. The temporary datastore is removed when the last VM for that datastore is unmounted.

The VM Management Job Summary report shows the virtual machine name, policy name, and user for live mounted virtual machines.


Live mounted virtual machines expire automatically based on policy settings. Users are notified of expiring VMs at 30-minute intervals, and virtual machines are unmounted automatically when they expire.