Those of you who dealt with cluster exchange servers in the past or present will remember and know the word failover. The fail over most of the time in Exchange word alarms the Exchange administrator unless administrator is failing over for maintenance in the scheduled window.
Remember Clustering you have Exchange Server A , you have Exchange server B , and use Microsoft clustering technologies to create Virtual Server which points back to “Active node”. So the idea here is clients who are using mail services connecting to Virtual server ( Virtual Server is mapping to Active Server) all databases and logs are being kept on the SAN backend, so if Active server goes down or gives up from shared resources the passive server jumps in and tales over the shared cluster resources.
If you pull up one of the user properties in Clustered Exchange environment, you will easily see the Exchange server is pointing to CMS server name which maps to Active server. IF Active server fails down the CMS is being taken over by passive node which becomes active and since clients are able to locate the CMS server, by using second server they access Exchange databases logs etc.
Here is the user who’s mailbox is configured on DAG
If you take look at this picture you will quickly see , “DB1” has two copies on two different server and if MAIL3 ( server) goes down the AD ( Active manager) will activate the same database on the Different server and users will still get connected.
The goal is to provide continuity to Exchange clients and keep them happy. Understanding how cluster works can easily be complicated to be honest, if you have never worked and not set it up by nature you may thing it sounds complicated and I hear you.
So what has been Changed in Exchange 2010?, beside Exchange 2010 is the fastest, greatest messaging application it is offering perfection and simplify in my opinion and you will understand more and appreciate this when you move into E210 (-:, trust me this isn’t advertisement it is a “FACT”.
What is DAG?
- DAG is boundary of mailbox database replication.
- DAG (Database availability Group) the name itself is servings it purpose, the new component & future build into Exchange2010 which provides high availability and site resilience. This mean to us if you have two exchange server configured as DAG member, if one server goes down, your helpdesk wont bombarded with user calls and your manager wont bug you (-: ….. ( we wish)
- Any server in a DAG can host a copy of a mailbox database from any other server in the DAG
- AM is new E210 component, Active Manager is an Exchange 2010 component which manages switchovers and failovers that runs on every server in a DAG.
*** setting up DAG is fairly easy to be honest, you will love the little steps and intelligent automation behind DAG once you start implementing it***
Understanding Active Manager
Understanding Database Availability Groups
Oz Casey , Dedeal
MCITP (EMA), MCITP (SA)
MCSE 2003, M+, S+, MCDST
Security+, Project +, Server +