Take a look at the "NTFS to Centera Migraiton" section of the "Symantec Enterprise Vault 8.0 Service Pack 3 (SP3) - Utilities.pdf" (http://seer.entsupport.symantec.com/docs/336838.htm)

Other quick thoughts...
Make sure the centera's are configured properly and PEA files in place. If you are going to implement replication then set it up and test it to make sure you can archive successfully to it.
Don't try to do it all at once... start with small blocks by date range and monitor peformance.
 

I agree with Rick. Create a test archive and archive from a test mailbox or a test file server for FSA.

The easiest way is after you have successfully tested it is to cut over the archiving to the Centera and then plan the migration of the already archived data over to Centera. 


Getting the security access to the Centera right is paramount so ensure that access is 100% before you make the cut over.

Also have you decided which model Centera you are going to use? Basic, Compliance or Compliance Plus. Each of them have their pros and some cons which you will need to address before making your purchase. Also EMC have released a Best Practice guide for archiving from Enterprise Vault to Centera which is well worth a look before you proceed with any implementation.

Here is the link to the Best Practices regarding EV and Centera mentioned in my earlier post

http://www.emc.com/collateral/hardware/white-paper...