Recovery Storage Groups Explained

Disaster recovery is one of the biggest problems facing Exchange Server administrators. Although Exchange is easier to recover than many other messaging systems, you must still deal with many small details to complete a successful recovery. More importantly, to ensure a successful restoration of service, you must prepare and test your recovery processes before you need them. One of the most common requests from Exchange customers has been a simpler way to handle common disaster-recovery scenarios. Microsoft has been listening, apparently, because Exchange Server 2003 contains a new feature that simplifies a common scenario--the recovery of one database.

Exchange Server 5.5 supports only one private and one public store per server, so recovering one database is logically equivalent to restoring the whole server. Exchange 2000 Server supports as many as 20 databases (four storage groups--SGs--with 5 databases each), but to restore one of these databases, you must fuss with a variety of Active Directory (AD) objects, which increases the complexity of the operation. Exchange 2003, however, introduces the Recovery Storage Group, a new kind of Exchange object that looks somewhat like a regular SG but has some important differences.

The Recovery Storage Group's purpose is simple: It lets you restore a database and its mailboxes without using a separate recovery server. This ability is invaluable when you need to restore just one mailbox. When you use an Exchange-aware backup program, the Recovery Storage Group lets you mount a mailbox database from backup onto any other Exchange server in the same administrative group as the server on which the original database resided. You can then copy data from the Recovery Storage Group's databases (however, you can't create new mailboxes in the Recovery Storage Group, and many regular SG settings are unavailable in Recovery Storage Groups). You can have one Recovery Storage Group per server.

The Recovery Storage Group works because the Exchange backup API transparently intercepts restored data; if a Recovery Storage Group exists, Exchange acts as though the Recovery Storage Group is the only SG on the server and directs all database restores to the Recovery Storage Group. You can then use our old friend ExMerge, which has received a makeover to support Recovery Storage Groups, to access a mailbox in the Recovery Storage Group--without first associating that mailbox with an AD user account. (The user account must exist, however, for ExMerge to access the mailbox data. Recovery Storage Groups won't solve the problem of losing mailbox data when you delete an AD account.) To return the Exchange Store to its regular restore behavior, simply remove the Recovery Storage Group.

Recovery Storage Groups provide a welcome improvement in Exchange recoverability. When you couple the Recovery Storage Group's "restore-anywhere" functionality with a solid backup strategy, you'll find that those occasional frenzied recovery sessions engender a little less panic. To learn more about Recovery Storage Groups, see the Exchange 2003 online Help (look for "Recovery Storage Group"). You can also expect to see whitepapers that describe the technology more fully from Microsoft and from third-party vendors who want to leverage Recovery Storage Groups in their products.