Exchange Server 2013, 2016 and 2019 Standard Edition can't mount databases that are larger than 1024 GB

Original KB number:   3059008


This issue occurs because the default database size limit for Microsoft Exchange Server 2019 Standard Edition, Exchange Server 2016 Standard Edition and Exchange Server 2013 Standard Edition is 1,024 gigabytes (GB). There is no default database size limit for the Enterprise Edition. The Exchange store checks database size limits periodically and dismounts a database when the size limit is reached. Therefore, this issue may occur after the database is automatically dismounted.

Additionally, when you perform a failover of the database, the failover fails.


The database maximum size is hard-coded as 1,024 GB in the event, even though you may have changed it to a higher value in the registry.


In order to have the full functionality of the Exchange database availability group (DAG) again, you must buy an Enterprise Edition license and apply it to the server.



Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify it, back up the registry for restoration in case problems occur.

To mount the database again, and to prevent the database from being automatically dismounted, follow these steps:

  1. Start Registry Editor.

  2. Locate the registry subkey: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<Server Name>\Private-<database GUID>.


    You can retrieve the GUID of a database by running the following command in the Exchange Management Shell:

    Get-MailboxDatabase -Identity "<database name>" | Format-Table Name, GUID
  3. If the Database Size Limit in GB DWORD value exists for the subkey, change it to the size that you want, in GB.

  4. If the Database Size Limit in GB DWORD value does not exist for the subkey, create a new DWORD value with that name, and then set its value to the size that you want, in GB.

  5. Mount the database on the server by using Exchange Management Shell and the -Force switch.


  • When you change this setting, the change is propagated to all servers that host a copy of this database.
  • This registry key may be deleted after an Exchange cumulative update is applied.
  • This registry setting still doesn't allow the automatic failover of databases within the DAG. You must use the -Force switch when you mount the database with this registry setting in place.


Microsoft has confirmed that this is a problem.