Exchange Server 2007 – High Availability
                                                             Local Continuous Replication

Whenever we talk about high availability what does it mean? It is nothing but keeping server alive as much we can. In Exchange 2003 or earlier version we had a concept called as clustering where we had a shared disk & Quorum Disk and in shared disk we use to store the exchange database & if one node fail other node will take the ownership.

In Exchange 2007 we have some new features in terms Exchange High Availability:

 Local Continuous Replication (LCR)
 Cluster Continuous Replication (CCR)
 Single Copy Cluster (SCC)
 Standby Continuous Replication (SCR) - It is only supported in Exchange 2007 SP1 version

We will take a walk on each and every  features which I described right now so that we can understand the basic concept and steps.

                                                            Local Continuous Replication (LCR)

LCR is one of the high availability source which is best suitable for making the availability of database from one disk to another disk, good to be used in small organization. It is a new feature in Exchange 2007. In one of my previous article I already explained you about LCR. Please go through it to know the theoretical concept.

My Current Topology:

I have one AD Server – DC\GC\DNS
One Exchange 2007 Server with sp1 – Hub & Cas Server Role
One more Exchange 2007 Server – Mailbox Server Role (exchange 2007 sp1)
 Inside Mailbox Server I have 2 Storage Group – 1 for mailbox database and 1 for public folder database.

Figure 1:
 

Now I am going to enable LCR for the  First Storage Group.
Note – Already I have created one test user for first storage group and I have send few mails to my test user which is located in the first storage group.

Now lets see the database size before we could enable LCR
Figure 2:
 

Enabling Local Continuous Replication through Graphical User Interface:

 Open the Exchange Management Console
 Expand the Server Configuration and then Mailbox
 Select the mailbox server and then click on First Storage Group
 Click on Enable Local Continuous Replication
Figure 3:
 

First Screen it will appear "Enable Storage Group Local Continuous Replication"
Figure 4:
 

After selecting the storage group we need to set the path to replicate the database and log file
I have choosed E Drive where I want to replicate the LCR database
Figure 5:
 

Note : in the above figure you will see only system path and log file path

In the next screen we will get the path to choose the database
Figure 6:

 

Then it will give summary about the configuration which we did and then we need to click on Enable
Figure 7:
 

After Enabling it will show you the summary about the configuration we did for enabling LCR
Figure 8

Lets check the database status
 Click on Storage Group i.e First Storage Group
Figure 9:
 

Note : Healty means continuous replication is happening and it is good in condition.

Now lets take a look on the copied database
Figure 10:
 

Additional Info: In the Adsiedit level under First Storage Group => Properties it will have attributes called as “msexcheseparamcopylogfilepath” & "msexcheseparamcopysystemlogfilepath" and in the mailbox database properties it will have one attribute called “msexchcopyedbfile” – Whenever we enable LCR.

Ok this is all about the configuration, now lets send few mails to thetest user who are located in the first storage group of mailbox store.

After sending mail the log file will store in the original database path then it will copy to the new location of LCR
Figure 11:

After a while see the size of the database on both the location. Inorder to know the replication process and seeding technology refer this link LCR

See the size of the database which is stored on the LCR it is getting increased from 8 Mb to 12 MB and still replicating because in the primary location the database size is 14 Mb..
Figure 12:

This is how you have enable through graphical user interface

Enabling LCR from the powershell command:

If you want to enable it from powershell, run this following command:
Let say if we want to enable local continuous replication for public folder :
 Open the Exchange Management Shell
 For seeding the database :
Enable-DatabaseCopy -Identity 'LCR\Second Storage Group\Public Folder Database' -CopyEDBFilePath 'e:\Second Storage Group\Public Folder Database.edb'
 Then Enable the log file continuous replication :
Enable-StorageGroupCopy -Identity 'LCR\Second Storage Group' -CopyLogFolderPath:'e:\Second Storage Group' -CopySystemFolderPath:'e:\Second Storage Group'

Figure 13:
 

Once you enable the local continuous replication and right click on storage group you will see some additional information
 Disable Local Continuous Replication – It will stop the LCR process. This disable option is choosed when you decide that you don’t want to have LCR anymore. Inorder to disable you can simply right click Storage Group and click on disable local continuous replication or else you can achieve it from Exchange management shell :
Disable-storagegroupcopy –identity ‘second storage group’
Note: Before you could disable LCR you need to move the all contents like log file and database from the copy stored drive to some other place or delete it. Because unless and until you won’t move it will not allow you disable. If you try to delete it manually it will create the database automatically because we have LCR enabled so that in scenario you need to suspend

 Suspend Storage Group Copy : To halt the replication process.
For suspending simply go with GUI or else from powershell:
Suspend-StorageGroupCopy –identity ‘second storage group’

 Restore Storage Group Copy : restore command is used to redirect the database path from actual production drive to the place holder of new LCR location i.e let say disk corrupted and need to have database backup so this is how we restore our database from the alternate location.
For restore storage group simply go with GUI or else from powershell:
Restore-StorageGroupCopy –identity ‘second storage group’

 Update Storage Group Copy :  This update is nothing but seeding your database manually. After the release of RTM beta version seeding is done automatically and there will certain time where we will come across in a situation to do the seeding manually so you need to run this command.
For update storage group simply go with GUI or else from powershell:
update-StorageGroupCopy –identity ‘second storage group’

Moving the Database Path:
Let says we need to change the database location of public folder database from one folder to another folder

 Right click the public folder database i.e. storage group then click on move database path, it will open the move database path user interface – just simply select the new folder for the database location and then click on move
Figure 14:
 

If you want to disable the local continuous replication simply right click the storage group and click on disable local continuous replication or from the powershell run this command : disable-storagegroupcopy –identity ‘second storage group’

How to view the status of Local Continuous Replication:
From Graphical User Interface:
 Open the Exchange Management Console
 Server Configuration
 Server (Where you have configured LCR)
 Storage group (which one you have configured)
 Right click it and go to properties and click on “local continuous replication” tab
Figure 15:
 

Or you can run ths command Get-StorageGroupCopyStatus -Identity ‘LCR\Second Storage Group’ from the powershell
Figure 16:
 

You have seen how LCR is replicated and how it is working, it is nothing but a log file shipping & replay technology but which service is responsible for doing log shipping. The service which is responsible for continuous replication is “Microsoft Exchange Replication Service”

Ok lets assume that disk got corrupted and I have LCR enabled.
Let me show you the print screen before disk got corrupted
Figure 17:
 

Now my disk got corrupted.

 Right click storage group and click on Suspend Storage Group : Figure 18
 

>  Right click storage group and click on Restore Storage Group
Figure 19:
 

 then it will give you configuration summary, simply click on restore
 Now it will restore the database i.e it will redirect the path of log file database to the new location which we have configured at the time of LCR creation
Figure 20:
 

Figure 21:
 

Note : it is showing my new location of the database and database is dismounted and at the same time it has disabled the LCR functionality.

Now let me show my outlook whether I am able to get the old message as per figure 17
Figure 22:
 

Conclusion:
This LCR is supported in both standard and enterprise edition and it will good solution for small business environment. Through LCR you can have the copy of the database as like RAID-1 Mirroring.

I hope this article is being very informative for you all. Thanks for sharing your time in the matter.

Reference Link:
Local Continuous Replication

Demystifying the Local Continuous Replication (LCR) feature

Upcoming Article:

Exchange Server 2007 – Cluster Continuous Replication (High Availability)

Exchange Server 2007 – Single Copy Cluster (High Availability)

Exchange Server 2007 – Stand-by Cluster Replication (High Availability)