The RSG is a newly added feature in Exchange Server 2003 for managing database restoration.
The RSG is a new type of storage group in Exchange Server 2003. This storage group is
specifically designed to allow you to recover mailbox store data without using a recovery forest
or recovery server. This not only speeds up data recovery but also lowers the total cost of
ownership for Exchange because you no longer need to purchase recovery hardware. Like
Exchange 2000, Exchange 2003 has a hard-coded limit of four storage groups per server.
However, because RSGs are a special kind of storage group, they do not count toward that limit.
Therefore, you can now create a fifth storage group called as RSG along with the four database
storage group. Prior to RSG, if you want to restore a store or storage group you must dismount
you existing storage group which gives you a downtime for network and users. With RSG you
are not require to do so.
Using RSG all the restore stores are put into RSG while the original mailbox remains online.
This is possible because the backup mailbox store is not actually added to the RSG. Instead, a
placeholder object is created in the RSG that is used as a reference back to the original store.
Once the store is mounted in the RSG, ExMerge.exe utility is then used to merge the data back
into the production mailbox store.
There are two primary uses for the RSG.
1. Recovering one or more individual messages from a mailbox: In cases when a message
cannot be recovered using the Recovered Deleted Items function, the RSG provides a
quick and effective way to recover the message(s).
2. Recovering from a corrupted mailbox store: There may be cases when restoring
messaging services as quickly as possible is of paramount importance. In this event, an
administrator can mount blank databases to restore messaging services, restore the
mailbox store to the RSG, replay the log files in the RSG if needed, switch the production
and RSG mailbox stores, and merge data from the newly created mailbox store into the
recovered mailbox store.