Disabling and Re-enabling Cluster Load Balancing During Avamar Hyper-V Backups

Avamar Hyper-V RCT backups may fail due to VMs Live Migrating during the Avamar Hyper-V backups:

avhypervvss Error < 43940 >: Failed to get the RCT extents for Virtual machine

Or

avhypervvss Error <43426>: Checkpoint creation for Virtual machine 'AVAMARPROD01v<GUID>' has failed and will be skipped from backup.

If a Hyper-V virtual machine (VM) resides on a particular cluster node, it gets added to that node’s vmgroup during the backup. If the VM Live Migrates to a different cluster node during the backup, it exists as a vmgroup member on the source node. Before the end of the backup, the Windows operating system attempts to remove the vmgroup. If the VM that Live Migrated previously is no longer running on the original source node, the vmgroup for that node fails to remove. This leaves the vmgroup orphaned as a result.

The Hyper-V plug-in cannot prevent Live Migration of VMs during the backup. The workaround uses PowerShell scripts to disable cluster load balancing before the scheduled backup job window. The next step is to create a PowerShell script to re-enable cluster load balancing after the backup job completes.

These scripts can be scheduled using the integrated Microsoft Task Scheduler application.

The scripts to disable and then re-enable cluster load balancing depends on the presence of System Center Virtual Machine Manager (SCVMM) in the customer's environment.

Steps for scheduling PowerShell scripts to disable cluster load balancing.

1. Open Notepad and copy the following lines into the document:

SCVMM in the environment

$HostGroup = Get-SCVMHostGroup "Hyper-V"
$DOConfig = Get-SCDynamicOptimizationConfiguration -VMHostGroup $HostGroup
Set-SCDynamicOptimizationConfiguration -DynamicOptimizationConfiguration $DOConfig -ManualMode

1. No SCVMM in the environment

(Get-Cluster).AutoBalancerMode = 0

Close and save as a PowerShell script file, with the file extension ".ps1."
For example, name this script as shown below to disable cluster load balancing before the Avamar Hyper-V scheduled backup job.

Disable_loadbalancer.ps1

2. Open Task Scheduler (Start > Windows Administrative Tools > Task Scheduler) on one of the Hyper-V cluster nodes.

3. Select the Task Scheduler Library and click the Create Task button:
   

4. Name the task and select the option Run whether the user is logged on or not, and enable the option Run with highest privileges:
   

5. On the Triggers tab, click New and select Daily option. Configure the scheduled start time to before or simultaneously to the time that the Avamar Hyper-V scheduled backup job starts:
   

   For example, if the Avamar scheduled backup starts at 5:30 PM everyday, then schedule the PowerShell pre-script to run at 5 PM.

6. On the Actions tab, click the New button.

• In the Program/script field, type PowerShell
• In the Add arguments field, type -File <<location of the PowerShell pre-script>>. 

-File C:\Temp\Disable_LiveMigration.ps1

7. Click the OK button to save the task.

Steps for scheduling PowerShell scripts to re-enable cluster load balancing

1. Open Notepad and copy the following lines into the document:

SCVMM in the environment

$HostGroup = Get-SCVMHostGroup "Hyper-V"
$DOConfig = Get-SCDynamicOptimizationConfiguration -VMHostGroup $HostGroup
Set-SCDynamicOptimizationConfiguration -DynamicOptimizationConfiguration $DOConfig -AutomaticMode

No SCVMM in the environment

(Get-Cluster).AutoBalancerMode = 2

2. Close and save as a PowerShell script file with the file extension ".ps1."

Reenable_loadbalancer.ps1

C:\Temp\Reenable_LiveMigration.ps1 ​​​