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Problem with Hyper-V virtual machine snapshot backup - GRT isn´t working V-79-57344-38721

Created: 16 Dec 2011 | 10 comments

Hello together,

I´ve a problem with Backup Exec 2010 R3 (with SP1 and all updates) on Windows Server 2008 R2. I´ve all licences installed because it´s the demo version, because the customer is testing Backup Exec to decide, if it is working or not and he has to buy MS DPM or he can use Backup Exec.

I´m going to backing up a few virtual machines on 3 Hyper-V Hosts (Microsoft Windows Server 2008 R2 with SP1 and up do date)

The snapshot backup of the virtual machine is working fine but the job completes with exceptions:

V-79-57344-38721 - Failed to mount one or more virtual disk images:

The Backup Exec Agent is installed on the Hyper-V server and in the virtual machines and is running as Local System. In the local security policy the right to "log on as a batch job" and "log onas a service" is given for the System, also the right to "create a token object"

If I start a normal backup of the server using the Backup Exec Agent, which is installed in the virtual machine, everything is OK, the agent is working correctly.

But a virtual machine snapshot backup isn´t working, the snapshot works (but I haven´t tested the restore of this yet) but the GRT in the VM isn´t working.

All requirements and configurations which are described in the Backup Exec 2010 Admin Guide are done!!

Have someone a tip or idea for me what to do?

Kind Regards,


Comments 10 CommentsJump to latest comment

sven88's picture

Hello Striker,

thank you for your post. I will check this next week when I´m at the customers office again.

Have a nice weekend!

sven88's picture


I´ve checked the settings of the VMs and I have 5 VMs with dynamic VHDs and 2 VMs with differential VHDs.

So 5 of the VM backups should run without any problem.

I´ve also checked the disk formatting which is described in the article you´ve send me, and this isn´t our porblem, we don´t use this 4k advanced disk formatting, the hardware is to old for this.

So, have you some other ideas, which can be my problem?

Kind Regards,


Striker 303's picture

Do you mean 5 Vm's without dynamic disks?

As dynamic disk are not supported for VM GRT backup - using hyper V agent.

sven88's picture

Hello striker303,

oh sorry, I misunderstood. I´m shocked, it´s a new information for me that dynamic disks are not supportet, because this is what the most virtual machines on Hyper-V servers are running, because it´s the recommendation of Microsoft for Hyper-V2 and Symantec isn´t supporting this with the Agent for Hyper-V :-(

But I didn´t find this information, that dynamic disks are not supportet in the admin guide. Can you tell me where to find this?

Kind Regards and merry X-mas,


pkh's picture

See the Hyper-V Storage Configuration Compatibility section on page 7 of the SCL.

BE 2010|2010 R2|2010 R3 Software (SCL)

See the second line.  Dynamic disks are not supported if you are using GRT. 

Steve Y's picture

Let's take a step back here.

When the word dynamic disk is thrown around when talking Hyper-V you have to be careful on what's dyanamic... ( The VHD) or (A volume/disk inside the guest).

Backup Exec support Dynamically Expanding disks (VHD' ). Meaning in Hyper-V you can have a Guest that has a Fixed or Dynamically Expanding VHD.

The Hyper-V Agent WILL NOT support VOLUMES INSIDE THE GUEST THAT ARE DYNAMIC volumes.  Meaning you logon to the guest and for example the D: drive is  a Dynamic Disk/Volume inside of the WIndows OS.

Striker 303's picture

Great!! Good explain Steve.., looks like I had confused Sven with "what's really dynamic"

sven88's picture

Hello Steve,

Hello Striker,

indeed you confused me with this dynamic disk. I thought you´re talking about the VHD Files.

Now I´m with you. We´re talking about the volume in the VM.

I´ve checked this and it´s the default option of Windows 'basic' volumes on all the VMs/Windows. Please see the attached screenshot.

It seems that there is another problem.

Kind Regards,


Steve Y's picture

Are all your guest failing with the below message?

V-79-57344-38721 - Failed to mount one or more virtual disk images:

Is this a backup to tape or disk?

Is the media server a virtual server or physical server if its a disk backup?