Tag Archives: DAG

Exchange 2013 Datacenter Activation Coordination (DAC) Mode

Datacenter Activation Coordination (DAC) Mode is a property of an Exchange DAG that is used to prevent 'split-brain' syndrome where multiple members activate their databases without knowing whether or not the other members have their databases mounted. What happens when DAC mode is enabled and set to 'dag only': After a failure of Exchange, Exchange will use the DACP protocol to determine the current state of a DAG and whether the databases should be mounted on a server.  DAC mode requires Read more [...]

Exchange 2013 DAG Latency requirements and considerations

According to Microsoft, Exchange DAG replication latency should be below 500ms roundtrip. This DAG latency requirement has limited my deployment options in the past to very specific WAN scenarios like MPLS, Point to Point Wifi, etc.  Many customers wishing to deploy a DAG across a VPN didn’t meet the latency requirements.  In other words, I haven't implemented an Exchange DAG that is replicating across the internet. From Microsoft: "Regardless of their geographic location relative to other Read more [...]

Reseed ‘Failed and Suspended’ DAG Database

Issue: One of your DAG databases is in a 'Failed and Suspended' state. Discovery: You may find this error via Exchange Management Console > Organization Management > Mailbox > Database Management > [select the database] > Database Copies Or you may see the following error in the event log on one of your Exchange Servers: MSExchangeRepl Event ID: 4113 Database redundancy health check failed. Database copy: DB1 Redundancy count: 1 Error: Passive copy 'DB1\EXCH02' is not in a good Read more [...]