Microsoft Exchange Server offers a lot of features when it comes to high availability, along with a combination of using Windows Cluster Service and Database Availability Groups (DAG). The DAG allows mailbox databases to be replicated between two or more servers, which are geographically located, for failover, resilience and disaster recovery. However, you must have a disaster recovery plan to cope with an untoward situation. At times, things might happen due to a software/hardware failure, sudden power outage, human error or any other issue.
In this post, we are going to look at an error which mostly happens when there is a problem with hardware, hosting the mailbox database or a problem with licensing. In each situation, the ideal solution is to move all the data to another location or consolidate it to another database. You might find that all the databases went offline and the users cannot access their mailboxes.
In such a case, the first thing you can do is check the state of databases with the Exchange Admin Center (EAC). You will find that the databases are unmounted. If you try to mount them, an error may occur.
Let’s start by checking the storage, where databases and log files are stored. Usually, the databases go offline when there is not enough storage on the drives. If the issue is due to the lack of storage, you need to talk to the virtual infrastructure engineers to extend or provision more storage for the databases. When the storage is increased, the database would mount automatically.
If this is not the case, you need to dig deeper by looking in the Application and System Log. The application event may give the following error:
event ID 225
At ’20/06/2020 5:00:10 PM’ the copy of database ‘DB02’ on this server was unexpectedly dismounted. The error returned by failover was “There is only one copy of this mailbox database (EX01). Automatic recovery is not available.”. For more specific information about the failures, consult the event log on the server for other “ExchangeStoreDb” events.
The error may be caused by a licensing problem. If you have more than 5 databases and using the Exchange Server Standard, licensing could be the issue, which is stopping you from using the other database. If this is the case, you have two choices:
- Upgrade to Exchange Server Enterprise, which is quite expensive
- Reduce the number of databases and consolidate the database, which is not mounting
Well, you cannot move the mailboxes from the database, if it is not mounted. You need to unmount another database so that you can mount the least populated database, do a database move of these mailboxes and remove the extra mailbox databases.
In another case, after looking at the System event, you may notice errors with regards to storage (see the example below).
The device, \Device\Harddisk6\DR6, has a bad block.
In such a case, it’s recommended to immediately move the databases to another drive. When a disk has bad block, it indicates that the drive will soon become faulty and immediate action is to be taken.
The action to be taken is creating a temporary storage to move the databases. This process includes provisioning the storage and creating a new database. Then you need to move the databases. Depending on the supplier’s stock and how fast you can provision the storage, there is a problem with the database move. If you have a lot of mailboxes, moving database could take some time. Until this finishes, it might be too late then.
To do a database move, the database should be in mounted state. If the database cannot be mounted due to licensing or the database is in dirty shutdown, there is no way to extract the data from offline database.
The native applications of Exchange Server do not offer extracting data from a database which is not mounted. Therefore, an alternative solution is to be quickly found, especially if you have a bad disk as time is of the essence.
When storage engineers or virtual infrastructure people have provided and extended the necessary storage, you would need to create the partition and format the disk. If the database is moved to a new storage and still it cannot be mounted, then there might be corruption in the database or log file. On the other hand, if you’re upgrading the license, you need to move the mailboxes from the unmounted database.
In such situations, third party applications such as Stellar Repair for Exchange come to your rescue as they can open any Exchange database format and version. By using the application, you can export mailboxes to PST and other formats. In addition, you can export data from damaged database directly to a live Exchange database. This will solve the problem of moving data from an unmounted database.