Hello
Due microsoft limitation is not possible restore Exchange 2010 database over Exchange 2013 server.
Exchange 2013 introduces a significant change from the VSS writer architecture used in Exchange 2010 and Exchange 2007. These earlier versions of Exchange included two VSS writers: one inside the Microsoft Exchange Information Store service (store.exe) and one inside the Microsoft Exchange Replication service (msexchangerepl.exe). In Exchange, the VSS writer functionality previously found in the Microsoft Exchange Information Store service has been moved to the Microsoft Exchange Replication service. The new writer, which is named Microsoft Exchange Writer, is now used by Exchange-aware VSS-based applications to back up active and passive database copies, and to restore backed up database copies. Although the new writer runs in the Microsoft Exchange Replication service, it requires the Microsoft Exchange Information Store service to be running for the writer to be advertised. As a result, both services are required to back up or restore Exchange databases.
About why DAG must be online, this is not clearly documented so seems to be a Microsoft limitation too.
To suit your needs, Data Protector offers different restore methods. You can choose among the
following:
• Repair all passive copies with failed status
• Restore to the latest state
• Restore to a point in time
• Restore to a new mailbox database
• Restore to a temporary location
You can specify different restore methods for different databases in the same session.
NOTE: The first three methods restore backup data to the original database and are therefore
only available if the original database still exists. The last two methods restore backup data to a
new location.
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I can guarantee you that before restore some powershell command are used for to discover current Exchange environment.
Get-MailboxDatabase
Get-MailboxDatabaseCopyStatus -Identity
If DAG is offline obiously it will fails. Therefore after migrate to Exchange 2013 if you want recoveer any Exchange 2010 database the best way is use temporally location and extrac data manually.
Best Regards