Joel Stidley's Blog : CCR

Using CCR to provide redundancy for Exchange Server 2007

Joel Stidley — Mon, 14 Jul 2008 19:14:18 GMT

About nine months ago I promised to blog about the different high availability options available in Exchange Server 2007. I followed up with a post on LCR but then abandoned the project. So, today lets start that series back up. This time around lets cover in detail what CCR is, how to use it and when you should and shouldn’t use it.

What is Cluster Continuous Replication (CCR)?

CCR is similar to LCR in the fact it keeps two copies of the databases on disk, however CCR is different in that it relies on Microsoft Clustering and a pair of servers. CCR has no single point of failure if configured properly, as there are two servers with two sets of everything. To take full advantage of having two copies of the data, on two separate servers, two separate storage systems should be used. Thankfully, Exchange 2007 has a lower disk I/O requirement than previous versions of Exchange, so that inexpensive local storage can often be used to ensure complete separation between nodes. CCR can only have two cluster nodes, an active and a passive node. Just like with LCR, you can only have one database in each storage group.

Configuration considerations

Since you do not need shared disk for a CCR cluster, you will most likely choose to use a file share witness rather than using a quorum disk. It is recommended to use a local Hub Transport server as the file share witness as being a file share witness will not put a substantial load on the server.

When would you use CCR? It is an excellent solution for environments that need local data redundancy and have the experience in working with Microsoft-base clusters.

Pros

No Single point of failure
Two copies of data exist at all times

Cons

Requires Microsoft Clustering Service
Requires double the disk space to store two copies of logs and data

What do you get when you add LCR, CCR, SCC and SCR? A very confused IT Manager!

Joel Stidley — Tue, 16 Oct 2007 14:36:00 GMT

I got a call from an IT manager today trying to spec out an Exchange solution for one of his companies that is moving from Novell GroupWise to Exchange. The customer has three sites and they have a requirement that if their connectivity between sites goes out that the users at each location would be able to continue to access their e-mail as well as send e-mail to each other.

So being the Exchange geek that I am I started spewing out the intricacies of LCR, CCR, SCR, SCC and I am pretty sure he was more confused than when we started talking. With all of the options and three letter acronyms what is a non-Exchange geek to do? Apparently not call me for advice!

To redeem myself I put together this guide on the availability options for Exchange mailbox server roles. This post is going to briefly describe each availability solution for Exchange.

LCR - Local Continuous Replication. This is a single server solution to provide data redundancy. You can run all of the server roles on this however there are some caveats for public folders. To be effective this solution requires two external drive arrays and two array controllers to provide true redundancy.
CCR - Cluster Continuous Replication. This is a two node cluster that relies on Microsoft Clustering Services. This does not require shared disk however would require a "witness" node. Other than the mailbox role, no other roles can be installed on the cluster. There active node of the cluster replicates all changes to a passive copy of the database. A minimum of three Exchange servers would be required (2 mailbox nodes and a non-redundant Client Access and Hub Transport).
SCC - Single Copy Cluster. This is a minimum two node cluster that relies on Microsoft Clustering Services. This requires shared disk like a SAN and has a single copy of the data. A minimum of three Exchange servers would be required (2 mailbox nodes and a non-redundant Client Access and Hub Transport).
SCR - Standby Continuous Replication (SP1). This allows replication of databases to other servers located anywhere on the Intranet. This replication can be done to and from any type of mailbox node (other than a mailbox server that uses LCR)

Now that we have the basic definitions set, look for four more posts in the next few weeks breaking down each of the mailbox high availability options for Exchange Server 2007 SP1.

Standby Continuous Replication SCR discussion at TechEd 2007

Joel Stidley — Fri, 20 Jul 2007 18:57:16 GMT

Harold Wong and Becky Benfield discuss how the new Exchange Server 2007 SP1 feature Standby Continuous Replication (SCR) works.

Becky shows on a whiteboard how replication works between CCR, Stand alone and how flexible the feature really is.

View the video here: http://msexchangeteam.com/videos/9/drandha/entry446453.aspx

Creating a CCR cluster article on OutlookExchange.com

Joel Stidley — Thu, 05 Oct 2006 07:43:00 GMT

Jason Sherry at OulookExchange.com posted an article about how to a CCR cluster. He goes step by step on through the whole process with a bunch of screen shots.

Check out his article here

And, no there is no direct relation between exchangeexchange.com and outlookexchange.com :)

Exchange 2007 CCR How to videos

Joel Stidley — Mon, 14 Aug 2006 04:46:00 GMT

One of the most promising new features of Exchange 2007 is Cluster Continuous Replication. This type of cluster enables new scenarios for being able to backup the "passive" node with your backup software without impacting production traffic or data. This essentially opens up your backup window to be 24 hours. No doubt there are a lot of questions on how to setup CCR. So the Exchange product group has created a video how-to on using CCR.

Take a look at the blog/video from Scott Schnoll here