In my last column, I wrote about the possibilities that Microsoft Exchange Server 2010 offers for running your Exchange organization without backups, and the topic generated a lot of good feedback (see "Going Backup-less with Exchange 2010?"). This week, I wanted to address some of that feedback to shed more light on the possibilities, and pitfalls, of going without backups.

First, Microsoft's Scott Schnoll wrote in to make an excellent point: Database availability groups (DAGs) alone don't really give you everything you need to go backup-free. That's why Exchange 2010 includes other features—notably, the new single item recovery feature, described at length in the Exchange Team Blog article "Single Item Recovery in Exchange Server 2010." 

Scott, and a couple of other correspondents, made a larger point, too. DAGs make it possible for you to perform backups less often. Typically, you'd make full and incremental or differential backups to be able to restore an Exchange database, but you can instead use the built-in DAG tools to give you the same degree of protection. However, in case of a total loss of a server, it might actually be faster to recover the server from a backup than to rebuild it from scratch and then let DAG replication restore the original data.

Another thing worth remembering is that DAGs can't protect public folder databases. That's not a huge problem because public folders already include multimaster replication. Whereas DAGs added replication to mailbox databases, public folders have had it since day one.

A couple of readers left comments to the effect that DAGs are too expensive to deploy in many environments because they require the Enterprise edition of Windows Server. One commenter said

Everything else about the Exchange 2010 storage story pushes the costs of high availability down—it's possible to use commodity hardware (SATA in some cases), no SAN, no RAID, etc. But we went from having the ability in Exchange 2007 to do replication on Windows Standard Edition with SCR and LCR (in combination with one another if desired) to having no HA or replication solution natively available on Windows Standard Edition in Exchange 2010.

I think this comment holds a kernel of truth. The Enterprise edition of Windows Server is indeed required to use DAGs, and it is much more expensive than the Standard edition. However, DAGs are closer in intent to cluster continuous replication (CCR), not the combination of standby continuous replication (SCR) and local continuous replication (LCR) that the comment mentions. If you compare the software license cost of a DAG implementation in Exchange 2010 with the cost of a CCR implementation in Exchange 2007, they're essentially equal—but the other savings that Exchange 2010 makes possible lowers the overall implementation cost.

There are many nuances to planning and implementing Exchange 2010 with DAGs that I'll be covering in the future. In the meantime, keep those cards and letters coming!

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