Uninstall Exchange Server 2013 Mailbox Role Fails With OAB Generation Server Error


Background

I recently purchased a new hard drive for server at home. It’s faster than old drives, and is perfect for my Exchange server 2013 virtual machines.  My existing environment consists of one Exchange 2013 CAS and two Exchange 2013 Mailbox servers in a DAG.  I plan to built two multirole servers on the new drive and decommission old servers gracefully.

Build/Remove

I successfully installed two multirole servers name MBX3 and MBX4, and added them into existing DAG. I removed database copies off old mailbox servers MBX1 and MBX2, and made sure they are not owning any databases. I then evicted them out of existing DAG, so Exchange 2013 binaries can be uninstalled properly.

Problem

MBX2 had no issue on uninstall process.

MBX1 was throwing a fit during pre-requisite check with following error message.

Error: This Mailbox server is responsible for generating an Offline Address Book. Removal of Exchange Server isn’t permitted.

For more information, visit: http://technet.microsoft.com/library(EXCHG.150)/ms.exch.setupreadiness.CannotUninstallOABServer.aspx  “

The link takes me to a technet page that has yet to complete.

In Exchange 2010, moving OAB generation server was quite easy. All you had to do is run Move-OfflineAddressBook cmdlet, and wait for AD to replicate.  In Exchange 2013, Offline address book is now generated by a system mailbox. See blog post from Exchange Team here.

First, i need to identify OAB generation server in a DAG environment.

Step 1: Identify the mailbox database hosting organization mailbox with OAB Gen capability.

Use the following command to list the arbitration mailboxes with persisted capability of OABGen and database on which this mailbox is hosted:

Get-Mailbox -Arbitration | where {$_.PersistedCapabilities -like “*oab*”} | ft name,database

Step2: Identify the mailbox server where the database hosting organization mailbox is mounted

Use following command to identify active copy of mailbox database:

Get-MailboxDatabaseCopyStatus DatabaseName

The server that where the database is MOUNTED, is the OAB generation server. In my case, it shows the correct server MBX3.

For kicks, I created a new standalone database on one of new server, and moved OAB system mailbox over with New-Moverequest cmdlet. Move was successful, however, the uninstall failed again with same exact error.

Solution

While I can always remove MBX1 manually by deleting it from ADSIEDIT, to take the easy way out, but I decide to check one more place in AD, the properties of each Office Address Book object.  For properties of ” \Default Offline Address Book (Ex2012)”I see this entry at bottom of the attribute list,

Image

OffLineABServer is still pointing to MBX1. After i manually changed it to MBX3, issue was resolved.

Conclusion

Though this setting was there in Exchange 2010, but move-OfflineAddressBook cmdlet changes it to new server. This is not possible in Exchange server 2013. You can still run the command, but it returns following error,

Image

Hopefully this will be fixed in the feature CU, that Exchange server setup ignores this setting,, and allows un-installation to succeed!

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