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Exchange Server - High Availability

Posted on 2011-02-15
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My goal is to have uninterupted email capability in the event of server hardware failure.  I currently have two Exchange 2003 Enteprise servers.  The second server currently is only an information store.  I have two main questions.

- is it reasonable to assume that if my 1st Exchange server would crash, I could redirect incoming and outgoing email to the 2nd server, assuming I make DNS changes as necessary?  Or am I missing something vital?

- If someone's mailbox was located on an information store that resided on the server that is down, can a temporary mailbox be created on the 2nd server Information Store?  I've tried this in the past and even though the Information Store is down, it says that user already exists.  This makes sense, but is there any way around this?  For instance, if my CEO's mailbox was on an information store that crashed, how can I get SMTP email to/from him until that store is brought back online?

Thank you
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Question by:tmeehling
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tigermatt earned 500 total points
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>> is it reasonable to assume that if my 1st Exchange server would crash, I could redirect incoming and outgoing email to the 2nd server, assuming I make DNS changes as necessary?  Or am I missing something vital?

Yes, but unless your two Exchange Servers are running in a cluster (which doesn't sound to be the case) only mail for recipient mailboxes on the 2nd server. Messages will be queued for recipients on the first server until such time that it comes back online, or they expire from the queue and get bounced back to the sender (whichever is sooner).

>> If someone's mailbox was located on an information store that resided on the server that is down, can a temporary mailbox be created on the 2nd server Information Store?

No. You'd have to drop the Exchange attributes on their existing user account and then re-establish a mailbox on the 2nd server. You might (possibly) have issues when the other server is brought back online, and at the very least would have to drop the temporary mailbox (including all its email) and reconnect the user to their real one on the first server.

What you really need for complete high availability is a cluster. If both your servers participate in a cluster, they are each capable of serving all your users. With Exchange 2003, you need shared storage (a SAN) to store the data for the cluster, and that can get pretty costly. If you don't already have this in place, I'd strongly recommend an upgrade to Exchange 2010, where you can use Database Availability Groups (DAGs) on two mailbox servers. DAGs use local server storage, are not as costly and (kudos to Microsoft) are one of the best clustering solutions I've ever worked with for Exchange.

-Matt
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by:tmeehling
ID: 34901382
Thank you very much for the clarity.  This is exactly what I was looking for.  Not necessarily the answer I wanted but pretty much what I expected.  I appreciate your expertise.
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by:tigermatt
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I just thought I ought to clarify a small point regarding my answer to your second question.

If the original server hosting the CEO's mailbox was still online, but the database was corrupted, you CAN give them a temporary mailbox using the so-called "dial tone" method on that same server. This involves dropping the existing mailbox database files from disk (or putting in a new, blank disk, if the RAID array holding the original database fell over). Blank mailboxes are created as the users log in, and they then have basic email functionality while you recover their data.

See: http://technet.microsoft.com/en-us/library/aa998947%28EXCHG.65%29.aspx.

I still can't see that working across the two servers, since the attributes on the user account would need to be changed to reference the other server as holding the mailbox, and as I said, that would get messy. However, I didn't mention this before but thought I should, because it's a possibility in some scenarios, depending on what failed. :)

-Matt
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