It depends what you need from the DAG. You can have several types of DAG - a "normal" DAG and a "Lagged Copy DAG", which is used more for disaster recovery.
How many replicas you should have is (in my opinion) more of a business decision than an IT one.
A "Normal" DAG is basically a copy of specified mailbox databases. You would have multiple replicas when you want failover to occur transparently to your end users. This allows several Exchange servers do go down (for maintenance or otherwise) and keep your mailbox database online.
A "Lagged Copy DAG" is still a DAG which replicates your mailbox database, but in a slightly different way. You can set a lag period on a lagged DAG so the replica is effectively a copy of the main database at some point in the past (by default 14 days, IIRC). Once a transaction log file is finished (i.e it reaches 1MB and another is created) on your active database copy, it is immediately copied to all lagged replicas but is not replayed immediately. This transaction log will stay on the lagged replica until the lag period expires, at which point it is written to the lagged copy database.
With that information, you should be able to give management an idea of what Exchange can do with regards to high availability/disaster recovery and possibly recommend a solution, but let them ultimately decide.
Move public folder data to Exchange 2010
Public folders are an optional feature in Exchange 2010. If all client computers in your organization are running Microsoft Office Outlook 2007 or later, then public folders are an optional feature. However, if Outlook 2003 clients are in use, then public folders are required. In addition, if you're currently using public folders for collecting, organizing, or sharing documents and other information and you want to continue doing so, you can use public folder replication to move your public folder data to Exchange 2010.
Learn more at: Understanding Public Folder Replication 28
How do I do this?
You can use the Exchange Management Console to perform this task.
- In the Console tree, click Toolbox.
- In the Result pane, double-click Public Folder Management Console. The Public Folder Management Console appears.
- In the public folder tree, click or expand Default Public Folders, and then select the parent public folder of the public folder that you want to move to Exchange 2010.
Note:
To configure replication for the offline address book (OAB) or for Schedule+ free/ busy information, expand System Public Folders, and then click OFFLINE ADDRESS BOOK or SCHEDULE+ FREE BUSY.
- In the Result pane, right-click the public folder you want to replicate to Exchange 2010 and select Properties.
- On the Replication tab, click Add to select an Exchange 2010 public folder database and then click OK.
- By default, Exchange uses the replication schedule configured for the public folder database. To create a custom replication schedule for the public folder, clear the Use public folder database replication schedule check box and select one of the settings in the list.
- To create a customized schedule, click Customize.
- To set the schedule, click the time grid in the Schedule dialog box. Public folder replication will run during the time slots that you specify.
- Click OK to close the Schedule dialog box.
- To specify the age limit for items in this public folder, type the number of days in the Local replica age limit (days) box. Items that have reached the age limit are deleted.
Note:
Age limits should be used for public folders only. They should not be used for System Folders, such as OFFLINE ADDRESS BOOK or SCHEDULE+ FREE BUSY.
- Click OK to close the Properties dialog and to save your changes.
- Repeat Steps 4-11 for each public folder you want to move to Exchange 2010.
How do I know this worked?
You can use the Get-PublicFolder cmdlet in the Exchange Management Shell to verify replicas on the Exchange 2010 public folder database. For example, to determine the replicas for all public folders in the public folder tree, run the following command:
Get-PublicFolder -Recurse | Format-List Name,Replicas
To determine the replicas for all system folders, run the following command:
Get-PublicFolder \NON_IPM_SUBTREE | Format-List Name,Replicas 29
Learn more about the cmdlet at: Get-PublicFolder
Visit Link : http://technet.microsoft.com/en-us/exdeploy2010/default.aspx#DeploymentCheckList/ee958313/2007
Best Answer
Ah, what happened to reading documentation?
I suggest a little read in http://technet.microsoft.com/en-us/library/dd298136.aspx
Storage groups are retired, did not work.
Database copies are that - backup copies of databases. You can basically have:
which, all in all, gives you pretty much a "never need the backup" scenario.
Now, creating another database is not exactly hard... http://technet.microsoft.com/en-us/library/dd298136.aspx has the command line methods for that.