Posts

CCR(Continuous Cluster Replication) in Exchange 2007 and why it is your optimal disaster recovery solution

With the design of Microsoft Exchange server 2007 Microsoft added some new HA or high availability options that were not available in the previous versions of Exchange.  I want to take the time to outline CCR or Continuous Cluster Replication and why it is one of the most anticipated features of Exchange 2007 and the best solution if you are looking for HA in your messaging infrastructure.
To begin there are basically two types of Exchange HA that you can implement.  DR, disaster recovery, or HA, high availability.  When it comes to these you have two very popular options.  The traditional option is SCC(Single Copy Cluster).  The latest feature of Exchange 2007 replaces this with CCR(Continuous Cluster Replication).  I will outline why CCR is a far superior choice over SCC.

  1. There exists no single point of failure.  When you implement SCC it requires a shared SAN which becomes your single point of failure. 
  2. Shared storage or a SAN is not a prerequisite for CCR.  However, if you go with an SCC solution you’re going to need to spend tens of thousands of extra dollars on a SAN solution.
  3. Mailbox server can span two locations.  This is probably one of the greatest accomplishments of Exchange Server 2007.  It has the ability to have a mailbox store at two locations.  If something happens to site A site B can pick up where it left off.
  4. Better failover design.  With CCR you maintain two independent copies of the log file and database data.  This is a big improvement and decreases chance the same failure will affect both servers.
  5. Easier to install.  Installation becomes easier since there is no shared SAN and the hardware requirements do not have to be identical
  6. Reduce load on your servers during backup.  Since your passive node contains up to date data on your Exchange database you can create your backup jobs on your passive node.  This means you can run backups mid day when the entire organization is hammering your active Exchange node.  This is completely seamless to the end user as they will notice no degradation while accessing the server.

How it works
 

     Exres.dll is gateway for clusters responsible for bringing resources online offline.

     Every 500 milliseconds UDP packet heartbeat

     Quorum resource is a shared disk that holds the configuration information all resources need access

Ccr requires:

     2003 Server Enterprise

     Two network cards

     Three hard drives OS/Logs/Databases

     Hotfix 921181 – Support for file share witness – http://support.microsoft.com/kb/921181

     Recommend Hub Transport for the file share witness

Install CCR

                Install x64 OS normally

                Join domain

                Isolate private nics to private vlan

                Hotfix 921181

Install IIS

                Install updated msdaps.dll

File Witness Share

                Create directory on hub transport

                Give the account which is used to run the cluster service full control of sharing and ntfs perms

Create cluster

                Go to program files administrative tools cluster admin

Create MNS Quorum

                Cluster res “majority node set” /priv mnsfileshare=servershare

                Cluster group “cluster group” move

                Cluster res “majority node set” /priv

Install Exchange 2007

                Heartbeat ports on the switch same vlan can be accomplished through port tagging

                Set-transportconfig enable configure transport dumpsters on hub transport server which is required

                Maxdumpstersizeperstoragegroup specify the max size of the transport dumpsters queue for each storage                          group 1.25 times the size of maximum message that can be set.

                Maxdumpstertime parameter is how long email message is in the transport dumpster so value of 7:00:00 7                        days means you can extended outage of 7 days and no loss of messages

Enable transport dumpster

                Set-transpotconfig –maxdumpstersizeperstorage group <size> -MaxDumpsterTime <timespan>

When installing Exchange 2007 make sure you have at least 3 hard drive arrays for the OS, logs, and database files.