Not able to download OAB when CAS-1 is down but CAS-2 is up
I am running a CAS array of 2 servers in Exchange 2010 in one AD site although each CAS is at a different location geographically speaking yet both servers are in the same subnet (we use layer 2 tunneling within our MPLS to accomplish that). In the backend we have a total of 4 MBX servers using DAG/DAC. When I launch Outlook 2007 and it connects to CAS-1 I am able to download the offline address book, when I shutdown CAS-1 and let CAS-2 take over, I don't lose my connectivity to Exchange but I am no longer able to download the address book, I get the default error of: Microsoft Exchange offline address book 0X80190194 I don't see a problem in the event viewer within CAS-2 even after I restart the File Distribution service. I navigate to C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\OAB and the directory is empty. Then I went to EMC and no matter where I go I cannot pull information about any of the 2 CAS boxes because apparently it's trying to connect to the CAS-1 IIS service and it's not up (since I shut it down for the purpose of testing). Shouldn't I be able to still retrieve information off IIS from CAS-2 since it's up? If I go to EMC > Server Configuration > Client Access > Highlight CAS-2 > refresh bottom pannel I get: The task wasn't able to connect to IIS on the server '***CAS1******.***.*****'. Make sure that the server exists and can be reached from this computer: The RPC server is unavailable. It was running the command 'Get-OwaVirtualDirectory'. Any help would be greatly appreciated. I want to make sure I'm not overseeing something here. I believe I should still be able to pull information off CAS2 even if CAS1 is down.
April 9th, 2010 7:29pm

Update: I restarted CAS-1 which then allowed me to nagivate through the EMC to Organization Configuration > Mailbox > OAB > Default OAB > Distribution > and added my missing server there (CAS-2). After I did this I noticed the directory of C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\OAB was now was populated with a copy of the OAB. So it was just a problem with not having the server as part of the distribution mechanism. The question still remains if I should be getting those IIS errors or better yet, should they be preventing me from manipulating settings for one of my CAS boxes if one of them happens to be down?
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April 9th, 2010 7:45pm

This is a known issue and has been fixed in SP1 for E2010. See: http://support.microsoft.com/kb/977966 Exchange 2010 EMC executes several commands to paint & populate the UI where it displays all Client Access Servers (Server Configuration : Client Access), like Get-OWAVirtualDirectory, Get-OABVirtualDirectory & Get-ActiveSyncVirtualDirectory. EMC executes these commands one by one for all CAS servers in local and remote sites & populates the related CAS servers after it receives the response to issued commands. If a CAS (in that list of several servers, it could be tens of servers for large customers or 2 in your case) is inaccessible due to any reason (down, being rebooted after installing updates, network issue, not responding due to any other reason, etc.), it will stop processing other servers and you will see errors (see text below). On top of that you will also experience significant delays, especially in ‘co-existence’ scenario, where multiple versions of Exchange Server are involved. The delay was estimated to be 7 minutes, for example, in one setup with Exchange 2010 & 2007 servers in 2 separate sites with 2 servers per site. The main reason for delay was the retrieval of related info from Exchange 2007 servers (legacy) in the other site. Microsoft Exchange The task wasn’t able to connect to IIS on the server ‘cas.contoso.com’. Make sure that the server exists and can be reached from this computer: The RPC server is unavailable. It was running the command ‘Get-OwaVirtualDirectory’. OK [An event with ID:4 will also be logged in ‘Application Log’ with this error] With the new fix in place, EMC handles the situation properly, it does not error out when it hits an inaccessible server, rather continues to look for other servers, plus it does not retrieve all properties (not all of them are really needed at first glance in the main UI, saves time & improves EMC performance) on first attempt to display them in the UI, rather display them when you bring up the 'Properties' page for a CAS. Sr. Program Manager, Product Quality Exchange Client Access Server
May 20th, 2010 7:36pm

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