Measuring Replication Health in a cluster

[Virtualization-Team]

First published on TECHNET on Dec 30, 2013

As part of running a mini-scale run in my lab, I had to frequently monitor the replication health and also note down the replication statistics. The statistics is available by by right clicking on the VM (in the Hyper-V Manager or Failover Cluster Manager) and choosing the Replication submenu and clicking on the View Replication Health… option.

Clicking on the above option, displays the replication statistics which I am looking for.

Clicking on the ‘Reset Statistics’ clears the statistics collected so far and resets the start (“From time” field) time.

In a large deployment, it’s not practical to right click on each VM to get the health statistics.  Hyper-V PowerShell cmdlets help in simplifying the task. I had two requirements:

• Requirement #1: Get a report of the average size of the log files which were being sent during the VMs replication interval
• Requirement #2: Snap all the VMs replication statistics to the same start time (“From time”) field and reset the statistics

Measure-VMReplication provides the replication statistics for each of the replicating VMs. As I am only interested in the average replication size, the following cmdlet provides the required information.

Measure-VMReplication | select VMName,AvgReplSize

Like most of the other PowerShell cmdlets Measure-VMReplication takes the computer name as an input. To get the replication stats for all the VMs in the cluster, I would need to enumerate the nodes of the cluster and pipe the output to this cmdlet. The Get-ClusterNode is used to get the nodes of the cluster.

$ClusterName = "<Name of your cluster>"Get-ClusterNode -Cluster $ClusterName

We can pipe the output of each node of the cluster and the replication health of the VMs present on that node

Get-ClusterNode -Cluster $ClusterName | foreach-object {Measure-VMReplication -ComputerName $_ | Select VMName, AvgReplSize, PrimaryServerName, CurrentReplicaServerName | ft}

Requirement #1 is met, now let’s look at requirement #2. To snap all the replicating VMs statistics to a common start time, I used the Reset-VMReplicationStatistics which takes the VMName as an input. However if Reset-VMReplicationStatistics is used on a non-replicating VM, the cmdlet errors out with the following error message:

Reset-VMReplicationStatistics : 'Reset-VMReplicationStatistics' is not applicable on virtual machine 'IOMeterBase'.The name of the virtual machine is IOMeterBase and its ID is c1922e67-7a8b-4f36-a868-5174e7b6821a.At line:1 char:1+ Reset-VMReplicationStatistics -vmname IOMeterBase+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidOperation: (Microsoft.Hyper...l.VMReplication:VMReplication) [Reset-VMReplicationStatistics], VirtualizationOperationFailedException + FullyQualifiedErrorId : InvalidOperation,Microsoft.HyperV.PowerShell.Commands.ResetVMReplicationStatisticsCommand

It’s a touch messy and to address the issue, we would need to isolate the replicating VMs in a given server. This can be done by querying only for those VMs whose ReplicationMode is set (to either Primary or Replica). The output of Get-VM is shown below

PS C:\> get-vm | select vmname, ReplicationMode | fl VMName : Cluster22-TPCC3ReplicationMode : Primary VMName : IOMeterBaseReplicationMode : None

Cluster22-TPCC3 is a replicating VM (Primary VM) while replication has not been enabled on IOMeterBase VM. Putting things together, to get all the replicating VMs in the cluster use the Get-VM cmdlet and filter on ReplicationMode (Primary or Replica. You could also use the not-equal to operation get both primary and replica VMs)

Get-ClusterNode -Cluster $ClusterName | ForEach-Object {Get-VM -ComputerName $_ | Where-Object {$_.ReplicationMode -eq "Primary"}}

To reset the statistics, pipe the above cmdlet to Reset-VMReplicationStatistics

PS C:\> Get-ClusterNode -Cluster $ClusterName | ForEach-Object {Get-VM -ComputerName $_ | Where-Object {$_.ReplicationMode -eq "Primary"} | Reset-VMReplicationStatistics}

Wasn’t that a lot easier than right clicking on each VM in your cluster and clicking on the ‘Reset Statistics’ button? :)