International Man of Awesome's Blog – When Too Much Awesome Isn't Enough

August 5, 2011

Decreasing Exchange 2010 DAG Failover Sensitivity by Increasing Cluster Timeout Values.

Filed under: Backups, Disaster Recovery, ESX, Exchange, Microsoft, Veeam, Virtualisation, VMware, vSphere, Windows 2008 R2 — internationalmanofawesome @ 2:21 pm

Whem running an Exchange 2010 DAG over a WAN, you may run into some of the limitations of Microsoft FCS (Failover Cluster Service). This service defaults to fairly low timeouts for fast failover in LAN environments. In a WAN environment, where latency may be higher, and some packet loss may occur, you may need to tweak the timeouts for FCS. I advise to tweak most of the settings via the FCS admin tool. However, there are a few settings to tweak via the command line, and here are the maximum values you can configure to make it “less sensitive”:

Exchange 2010 DAGs use Windows Failover Clustering. By default, FCS has fairly low timeouts that are ideal for use in fast localised LAN environments

If you operate your Exchange 2010 DAGs over a WAN where issues such as latency and packet loss can occur, you may find that your email databases are failing over. By default, heartbeat frequency (subnet delay) is 1000ms for both local and remote subnets and when a node misses 5 heartbeats (subnet threshold) another nod within your DAG cluster will initiate a failover.

You can change these values to their maximums by issuing the commands below on a DAG mailbox server in a command box.

cluster /prop SameSubnetDelay=2000:DWORD

cluster /prop CrossSubnetDelay=4000:DWORD

cluster /prop CrossSubnetThreshold=10:DWORD

cluster /prop SameSubnetThreshold=10:DWORD

You can check that the properties have been applied by executing the following command on a DAG mailbox server in a command box.

cluster /prop

If you virtualise your Exchange 2010 mailbox servers, this may also assist in preventing failover when backing up your VMs using backup products that take snapshots of your VMs like Veeam Backup and Replication. Note that doing backups in this manner is NOT supported by Microsoft at this time.

Reference – Configure Heartbeat and DNS Settings in a Multi-Site Failover Cluster –



  1. […] A little bit of research let me to this site.… […]

    Pingback by VMware vSphere 5 snapshot caused DAG to failover | ronnie's blog — October 29, 2012 @ 10:13 am

  2. When you backup Exchange 2010 using Veeam Backup and Replication with Application Aware Imaging Processing turned on it uses Microsoft VSS to backup up Exchange which IS supported by Microsoft.

    Comment by Zoltan — April 5, 2013 @ 12:02 am

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