While the Schema Migration Utility (commdirmig) is running, Messaging and Calendar servers can stay online and continue to look up user entries in the LDAP directory. (However, no provisioning should take place during the migration.)
In addition, commdirmig provides the following safety features that let you control and stage the migration:
You can migrate one domain (or selected domains) at a time.
By default, commdirmig operates in preview mode (performs a dry run). The commdirmig utility writes an LDIF-formatted audit file containing the changes to the directory data that would be made during an actual migration. The LDAP directory itself isn’t changed.
After the utility executes in preview mode, you can examine the LDIF audit file and review the intended changes to the directory data.
When you are satisfied that the changes are correct, you can use the ldapmodify tool to apply the LDIF entries to the LDAP directory. Or you can run commdirmig again in online mode, which directly migrates the directory data to Schema 2.
The commdirmig utility produces an undo file, which you can use to roll back the changes made to the LDAP directory.
If the migration is interrupted, you can run commdirmig again. The utility will resume the migration without changing any data that was properly migrated.
The DC Tree is not used in Schema 2, but it does no harm to leave the deprecated DC Tree in the LDAP directory after the data has been migrated to Schema 2.
After you have completed the entire migration process, you can choose to remove the DC Tree with an LDAP command-line tool. Before you remove the DC Tree, be sure to verify that the migration was successful.