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Migrating Level-4 OEM to New Datacenter With Zero Downtime

Written By askMLabs on Thursday, December 15, 2016 | 10:01 PM

I am working on a project to migrate a level-4 OEM(Oracle Enterprise Manager) running on Oracle Database Appliances(ODA) from one Datacenter to another Datacenter. I am also planning to write a white paper on this and will  submit to Oracle.

I proposed the following action plan to migrate these ODAs to new datacenter with zero downtime. 

I am going to explain the outlined procedure to perform this activity in the present article, but will also write some more articles on the same topic with detailed step by step procedure.

In order to understand this article, Please note the following keywords.
  • OEM - Oracle Enterprise Manager
  • ODA - Oracle Database Appliance
  • OMR - Oracle Management Repository ( Oracle Database )
  • OMS - Oracle Management Service
  • OMA - Oracle Management Agent
  • PDC - Primary Datacenter
  • SDC - Second Datacenter or Standby Datacenter
  • TDC - Third Datacenter
  • DNS - Domain Name Service

Present Setup : 
  • Two primary ODAs with OEM 12c installed - At PDC
  • Two secondary ODAs with OEM 12c (Standby with ASM replication from primary for OMS binaries) - At SDC
  • Database and Grid are on
  • Oracle Database is two instance RAC both on primary and secondary
  • ODAs are with old control version (oakcli)
Targetted Setup : 
  • Two primary ODAs with OEM 12c - At PDC 
  • Two secondary ODAs with OEM 12c (Standby with ASM replication from primary for OMS binaries) - At TDC
  • Database with and
  • Grid with ( without flex ) 
  • Oracle Database is two instance RAC both on primary and secondary
  • ODAs with the latest control version ( oakcli )


  • Primary ODAs at PDC are hosting OEM12c with version. The database is RAC and it has two OMS services  running.
  • Secondary ODAs at SDC are standby for Primary and it hosts the same versions as primary.
  • The primary to secondary OMS replication is setup using ASM file system. So it is ASM replication from primary to secondary. ( Note that it is not standby weblogic setup ) . Please read my other article on how to convert Standby weblogic Server setup to ASM replicaiton.


  • The secondary datacenter SDC will be replaced with a third datacenter TDC. So we got new ODAs and they are stacked and installed at new datacenter. These ODAs are called toda01 and toda02. The next step is to create a new standby database at TDC with primary database at PDC.
  • Grid software will be
  • Database software will be and ( Need to install both the binaries, so that the latest version can be used for database upgrade)
  • In this step, we are going to create a new standby database TOEMDB for the primary database POEMDB. At this point of time, we have  two standby databases up and running. We need to make sure that the archive logs are shipped to both the standby locations. Once the second standby database is created, we need to prepare the toda's for the OMS creation.
  • We need to prepare the ODAs at TDC for ASM replication. The procedure and detailed steps will be posted in a different article. 
  • Disable the ASM replication from PDC to SDC.
  • Enable the ASM replication from PDC to TDC.
  • Note that, at this point, we still have two standby databases, but only one ASM replication from PDC to TDC. The DNS is still pointing to SDC.
  • Now the standby setup for database at SDC can be disabled. Need to remove all the configurations for SDC standby database at primary database running at PDC.
  • Now primary database is at PDC and One Standby Database is at TDC. Primary OMS is at PDC and Standby OMS is at TDC.
  • DNS ( loadbalancer ) updates need to be done to reflect the new ODAs at TDC. All the references for ODAs at SDC should be removed from DNS and loadbalancer.
  • We can now switch off or decommission the ODAs at SDC as per your enterprise standards.
  • At this point, we have PDC as primary OEM and TDC with the standby OEM setup.
  • Database at PDC is with and at TDC with Note that we still have binaries created for future database upgrade.
  • Grid at PDC is and Grid at TDC is
  • ODA control software oakcli is with old version at PDC and at latest version at TDC.

  • The OEM setup looks as shown above after completely replacing the SDC datacenter ODAs with TDC ODAs.

Now we are going to repeat the same steps for replacing the ODAs at PDC. For this replacement, we are using the same datacenter PDC. So in the same datacenter PDC, we will replace the old ODAs with the new ODAs. For this to perform ,we need to switch the roles of the present OEM.

  • Rack and stack the ODAs at FDC.
  • Database with version and
  • Grid wit h12.1.0.2 version.
  • Swith the roles of the OEMs at PDC and TDC.
  • Once the OEM at PDC is standby, we can repeat the same steps from 1-7.



  • When the ODAs at PDC are replaced completely with new ODAs, we can switch back the roles. So that, ODAs at PDC will run the primary OEM and PDAs at TDC will run the standby OEM.

The Complete procedure is shown in the following flow diagram for easy reference to understand what we are doing at each stage.

Hope this information helps you to understand the migration of  Level-4 OEM with zero downtime.

Please comment or reply to me if you have any questions or doubts.

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