In Exchange Server 2010 RTM, a user's mailbox and archive mailbox both reside in the same mailbox database. Exchange 2010 SP1 allows you to decouple archive mailboxes and place them into alternate databases. As a result, many organizations can create databases containing only archive mailboxes, also called archive databases.
Administrators usually create an archive database out of storage concerns. Most organizations enforce storage quotas on users' Exchange mailboxes to limit the number of retained messages. When Microsoft introduced personal archives, a lot of administrators liked the idea of having a secondary message repository but were concerned with how much storage space the archives would consume.
One way to get around the issue of limited storage space is to place your archive database on low-cost storage. An archive database likely won’t create the same I/O demands as a user's primary mailbox. That means you can use low-end servers with inexpensive Serial ATA (SATA) drives for archive database storage. These servers provide plenty of storage space and won't break the bank.
Using low-end hardware, however, can be problematic if you introduce database availability groups. DAGs don’t distinguish a database that contains archive mailboxes from one that contains user mailboxes. That means you can place an archive database into a DAG without any initial problems. But DAGs require each database copy to use the same storage path, which can be an issue if the archive server is using SATA storage.
You’ll also need to provide enough storage space for each server in the DAG to store a copy of the archive database. This undermines the benefits of purchasing low-end hardware for the archive server.
Some Exchange organizations don’t include an archive database in the DAG. This can be a mistake since it can lead to a single point of failure and can cause rules to fail. For example, it’s common to configure rules that automatically move certain types of content into users' archive mailboxes. If the host server fails, any applicable rules will fail as well.
If you have already committed to using low-end hardware for your archives, I recommend purchasing some additional low-end servers with inexpensive storage. Use those servers to create a DAG specifically for your archive database; this will protect archives from failover without having to worry about consuming storage space or IO cycles on primary mailbox servers. The existing DAG can continue to service databases containing user mailboxes, while the new DAG is dedicated solely to user archives.
ABOUT THE AUTHOR:
Brien Posey is a seven-time Microsoft MVP with two decades of IT experience. Before becoming a freelance technical writer, Brien worked as a CIO for a national chain of hospitals and healthcare facilities. He has also served as a network administrator for some of the nation’s largest insurance companies and for the Department of Defense at Fort Knox.