When disaster strikes your Microsoft Exchange Server organization, your first instinct may be to reach for your backup. However, restoring a backup may not always be the best course of action. That's because when a failure occurs it is important to restore mail flow as quickly as possible, and restoring a backup can be time consuming. It is usually better to restore mail flow first, and restore the rest of the data later.
Rebuilding the Exchange Server infrastructure
When an Exchange Server failure occurs, the first thing that you must do is to identify which server has failed and what roles that server was hosting (assuming that the server is running Exchange 2007 or Exchange 2010). The configuration information for every Exchange Server role except for the Edge Transport Server role is stored within the Active Directory. This makes it possible to rebuild the server without restoring a backup as long as your Active Directory is still functional.
The first step to take is to open the Active Directory Users and Computers console and reset the computer account that belonged to the failed server. But don't delete the computer account or you will not be able to recover the server.
When the computer account has been reset, install Windows Server onto the failed server (or onto a replacement server). You must use the same Windows edition and the same service pack as what was running on the failed server. Once Windows has been installed, you must change the computer name to match the name of the failed server. After doing so, join the server to your domain. Once you join the server to your domain, the server will assume the identity of the failed server.
Next, insert your Exchange Server installation media into the server (this also has to match the version and service pack level of the failed Exchange Server). Rather than performing a typical Exchange Server installation, open a Command Prompt window, navigate to the installation media and run the following command:
This command will rebuild the failed server within a few minutes. Once the server is rebuilt, be sure to install any missing patches.
Restoring mail flow to the Exchange Server
If the failed server was running any server role other than the mailbox server role or the edge transport server role, then you should be back in business. However, if the failure occurred on a mailbox server, then mailbox database may have been lost. The best thing to do in this type of situation is to perform a dial tone recovery.
A dial tone recovery is a technique where you create a database filled with empty mailboxes. That way, users can begin sending and receiving mail without having to wait for hours or days while you restore their old messages.
The technique for creating a dial tone database varies slightly depending on what version of Exchange Server you are using. In Exchange Server 2010, you must begin by creating an empty database using the New-MailboxDatabase cmdlet. For example, you might type:
New-MailboxDatabase --Name DialTone --EdbFilePath D:\Dialtone\DialTone.edb
Be sure to create the database in a location that has plenty of free space since you will eventually merge the user's old data into the database.
Once the new database has been created, you must rehome your user accounts so that they point to the dial tone database. To do so, you must use the Get-Mailbox command to retrieve a list of all of the mailboxes that were stored in the failed database (this information is stored in the Active Directory). You must then use the Set-Mailbox cmdlet to rehome the mailboxes. For example, if your old mailbox database was named DB1 then the command that you would use is:
Get-Mailbox --Database DB1 | Set-Mailbox --Database DialTone
The last step is to mount the database; then the users will be able to send and receive mail. You can mount the database by using the Mount-Database cmdlet. In this particular case the command that you would use is:
Mount-Database --Identity Dialtone
Recovering data from the Exchange Server
The last step in the process is to recover your old data. The method you should use for this process varies depending on what version of Exchange you are using. In Exchange 2010, you would create a recovery database. In Exchange 2007, you would have to create a recovery storage group. From there you would restore the backup of your mailbox database to the recovery database or recovery storage group. When the process completes, you will have to merge your recovery database or recovery storage group with any data that has accumulated in the dial tone database. At the Microsoft TechNet website, you can find instructions for performing a dial tone recovery in Exchange Server 2010 and Exchange Server 2007.
Ultimately, the steps that you will have to perform during an Exchange Server disaster recovery operation will depend on the nature of the failure. This article assumes that at least one Exchange Server has failed catastrophically. If the failure is less severe, then you may be able to omit some of the steps that I have discussed.
About the author: Brien M. Posey, MCSE, has previously received Microsoft's MVP award for Exchange Server, Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. You can visit Brien's personal website at www.brienposey.com.This article was previously published on SearchDisasterRecovery.com.
This was first published in January 2011