This guide simply explains in a very easy way, all the technologies and procedures that you need to know to perform Exchange 2010 data center switch over, recovering DAG member or stretching DAG between sites.
Check other parts:
1. Introduction Part
Defined as a mechanism to ensure that only one subset of members are functioning at any given time. It is used to find majority.
There is Quorum data that is configuration shared between all nodes.
Exchange 2010 supports only two out of four models of Quorums:
- Node Majority: for odd number of nodes
- File share majority: for even number of nodes
Witness is a file share (Witness.log) that represent a vote when there is a need to break the tie. When we are one vote from losing the majority, the node that holds the cluster group (PAM) will lock the witness file share.
The witness cluster file share is created when the DAG members become even and cluster will apply isalive controls to monitor it. If it fails, the cluster group is moved to another node and try to bring it online.
(Exchange Subsystem) group should be member of the local administrator group on the witness server and the alternative witness server.
1.2 DAG Networks
For each subnet that the cluster discovers, a DAG network is created. Note also that heartbeat happens in all networks.
Two types of DAG Networks:
- MAPI Network:
o You can have only one MAPI network.
o Default Gateway and register in DNS
- Replication Network: (Over TCP 64327)
o You can have Zero or as many replication networks as you much
o No default Gateway and no register in DNS
It is important to note the following:
o DAG Network enumeration happens only when adding DAG members or can be triggered by running (Set-DatabaseAvailabilityGroup –DiscoverNetworks)
o If the MAPI network dies in a server, automatic switch over happens.
o If Replication network dies in a server, replication will happen over MAPI network.
o ISCIS network should be configured to be ignored from Cluster use.
And also make sure that the replication cannot route to the MAPI network in any case, or cross heartbeat scenario will happen.
1.3 Active Manager
Lives inside (Microsoft Replication Service)
The data about where the database is active now DOES NOT LIVE IN Active Directory. Active Manager is the one who knows about it.
Three Server types:
- Standalone ( for nodes not member of DAG)
- Standby (SAM)
- Monitor local resources and notify PAM
- Give information to Active Manager clients about where databases are active
- Primary (PAM)
- The one who holds the cluster group
- Best Copy Selection
Active Manager Client exists in HUB and CAS to know where the active copy lives in order to deliver or access data.