The Duplicate Computer Merge task will merge Asset and Inventory computers based on a merge key. This task is useful and will only work for when computers are brought in using the following ways:
 

1. An unmanaged computer (that does not have an Agent installed yet) has been brought in using a Data Connector Import Rule, a sync from Barcode or been manually created using the CMDB Edit user interface. This has also had its key field populated, such as its Serial Number.
2. Later, an Agent is installed. Two duplicate now exists once the Agent checks into the server and creates a record (which may take upwards to an hour), but does not yet include Inventory Solution data classes to enable the merge to work.
3. Later yet, an Inventory Agent plug-in is installed and this returns the Inventory Solution key field to match on, such as its Serial Number. Note: This serial number is not to be confused with any serial numbers reported by Core or other Solutions, such as may be found in various areas of a computer's Resource Manager data.
4. The two duplicates now contain the required data classes and should successfully be able to be merged using the Duplicate Computer Merge. Note: Formerly, in Notification Server 6, the Core hidden task, "NS.Merge Duplicate Records", used to perform this, however, with Symantec Management Platform 7.1 and higher, this task no longer is responsible for this. Therefore, the Duplicate Computer Merge task from CMDB should be used instead.

The Duplicate Computer Merge task has several requirements:
 

• This task does not merge duplicates found in only one of the solutions, such as merging an unmanaged and an unmanaged computer, or a managed and a managed computer. Use the Resource Merge Rule task for this scenario.
• This task only merges two records maximum of each duplicate, one duplicate Asset, another duplicate Inventory computer. If more than one duplicate exists of either type, also use the Resource Merge Rule task instead.

• This task is not designed to use a Serial Number from Core. This may be perceived as a duplicate, but this task will not work with it. Instead, once again, use the Resource Merge Rule task for this.
  
  The following SQL script can be used to help verify if a specific computer will be merged if it has duplicates that match this criteria. Note: Results do not necessarily indicate the presence of duplicates, only that a computer has been found with both an Inventory and CMDB Serial Number. If duplicates exist, and they share the same Serial Number, then the Duplicate Computer Merge should successfully merge both records.
  
  USE Symantec_CMDB
  SELECT vc.Guid, vc.Name 'Computer', isn.[Serial Number] 'CMDB Serial No.', ihcs.[Identifying Number] 'Inventory Serial No.'
  FROM vComputer vc
  LEFT JOIN Inv_Serial_Number isn
  ON vc.Guid = isn._ResourceGuid
  LEFT JOIN Inv_HW_Computer_System ihcs
  ON vc.Guid = ihcs._ResourceGuid
  WHERE isn.[Serial Number] IS NOT NULL
  AND ihcs.[Identifying Number] IS NOT NULL
  ORDER BY vc.Name

Additional Information
 

• The Duplicate Computer Merge task is not scheduled or running by default. Set up an appropriate schedule for this after it is assumed that all CMDB and Inventory has finished processing.
• If a Duplicate Computer Merge includes an Exclusion Filter, this may accidentally be removing records for evaluation, not enabling them to be merged. Review what the filter in question includes. If it has duplicates, this filter shouldn't be used as an exclusion.

Related Article

How to troubleshoot duplicate assets
http://www.symantec.com/business/support/index?page=content&id=HOWTO5773