Information and announcements from Program Managers, Product Managers, Developers and Testers in the Microsoft Virtualization team.
In Windows Server 2012 Release Candidate, Hyper-V administrators can monitor the ‘health’ of the replicating VMs using the Replication Health attribute. This property allows administrators to answer common questions such as:
The two-part FAQ post explains the concept of Replication Health and provides guidance on how to interpret the attribute values.
Replication state shows the current state of the replicating VM. It indicates whether the VM is being replicated, whether initial replication is pending etc.
ReplicationState can be queried from:
The table below captures the states as seen in WMI, UI and PowerShell.
VM is not enabled for replication.
Pending Initial Replication
Replication relationship has been created but Initial Replication has not been initiated. This is seen on the primary VM only.
The replica VM enters this state when a replication relationship has been created but Initial Replication has not been initiated (or) Initial Replication is in progress.
The primary VM enters this state when Initial Replication is in progress.
This state (on both the primary and replica VM) indicates that the replication is ‘Normal’.
Prepared for planned failover
This state is applicable only for the primary VM. It indicates that Planned Failover is complete and that the VM is locked from powering up.
Failover has been initiated on the replica VM but has not been completed. The Failover operation is considered to be complete only when the VM is either reverse replicated (or) when additional recovery points are removed.
The replica VM enters this state once the Failover operation has been completed.
The VM enters this state when replication is Paused. This state is applicable on both the primary and replica VM
This state is applicable on both the primary and replica VM and indicates that replication is not occurring on either VM. Usually administrator intervention is required to restore replication.
The primary VM enters this state when it needs to be resynchronized.
Resynchronization has been initiated on the primary VM.
If the primary VM suspends the resynchronization operation, the VM enters this state.
Good question! While Replication State is comprehensive, it provides the current replication status – it does not provide any ‘trending' information or warnings to watch out for.
On the other hand, Replication Health provides an aggregated view of events in a certain interval. Hyper-V Replica uses inbuilt heuristics to warn the administrator that replication is sub-optimal.
Let’s consider an example where your organization’s network connectivity is over burdened between 2am to 6am everyday. This could result in a sub-optimal replication of the VM (i.e replication is not occurring every 5mins or the replica VM is behind the primary VM by more than an hour). When you check the Replication State of the VM at 10am everyday, it would indicate that replication is normal (Replication Enabled, as described in the above table).
However, this does not paint a true picture as your replica is behind the primary VM. Replication Health on the other hand would either be set to Warning or Critical which would prompt you to debug the issue further.
Q4: Ah, so what are the possible values for Replication Health?
Hyper-V Replica aggregates these events into 3 potential values which can be queried from:
This state is observed when the VM which is not enabled for replication.
Replication is normal, see Q7 for more details.
Replication is not normal. See Q6 for more details on how to interpret this state.
Replication is not normal or optimal. Administrators need to intervene to fix and resume the replication. See Q5 for more details.
The Replication Health is flagged as Critical if one of the following occurs:
In the Replication Health pane, click on ‘View Events’ to see a filtered set of events corresponding to this VM which helps you root-cause the issue.
The Replication Health is shown as Warning when the replication is ‘not optimal’. The conditions which would result in a Warning health include:
Q7: So does ‘Normal’ mean that the replication is on track?
Correct, this health indicates that replication has the following characteristics:
We will cover further details such as PowerShell cmdlets, tips to extend the platform capability to monitor the health by setting up alerts, interpreting the attribute in the Replication Health view, concept of a monitoring interval, monitoring start time etc., in the next post.
Another point is on the "Critical" state. Why a primary vm enters into Critical state if an administrator pauses replica VM?
The 'Critical' state signifies that the replica copy and the primary VM are off significantly out-of-sync. This may be caused due to an user action or due to an infra issue (eg: networking problems). In either case, we bring it to the user's attention that the replication cycles have been missed.