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On my Win2008 R2 clusters there is a performance counter called Cluster Multicast Request-Response Messages\Messages Outstanding.

Solarwinds includes it as a monitor on their Failover Clustering application template. One of my Hyper-V nodes keeps having this alarm go off (value greater than 0). I'm willing to remove this counter from the monitor but want to understand what it means first.

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There is a Failover Clustering Performance Counters blog post on MSDN that describes the different Performance counters that are available.

Multicast Request Reply is a communication primitive that we have in the cluster. You can think of it as an RPC that allows you to send a call to multiple recipients and then get response from all of them. This component also has an internal queue. Messages Outstanding tells you the length of this queue. Usually it is close to 0. Messages Sent shows how many MRRs we have sent since the server has been running, and the Delta tells you what the change is since the last sampling interval.

There are many components in the cluster that are utilizing MRR. One of the heavy MRR users is Cluster API. For instance when you run Get-ClusterResource using PowerShell, all the resources are displayed and the cluster has to communicate with the current resource owner to query the resource state. This communication is done using MRRs.

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