A. Exchange 2010 introduces a new archiving capability. With the archive, users have a second mailbox, the archive mailbox that exists in the same Mailbox database and is available from both the Outlook client and Outlook Web Access. The Archive mailbox is associated with the user's primary normal mailbox and the management of the archive and primary is identical. The primary mailbox is available online and offline and its content is stored in the Outlook OST cache file. The archive mailbox isn't cached on the user's local machine and is therefore only available online.

The online-only storage is the point of the archive. As you increase the size of mailboxes, you don't necessarily want all the data stored locally on user machines, because it can lead to very long initial download times when users get a new machine. The data users frequently access is stored in the primary mailbox, which is ideally less than 10GB and is cached locally. Everything else is stored in the archive mailbox and available online, so it can be much larger and contain historical data. Because the archive mailbox is part of the same mailbox database, its availability is the same as the primary mailbox (i.e., it will be replicated as part of a database availability group).

The user experience for the archive is intuitive. Users will see their mailbox and their archive mailbox. They can drag and drop a PST file into the archive and the PST will be imported into the archive automatically, or users can schedule the import to happen at outside of working hours. The viewing and navigation of the primary and archive mailbox is the same. If a user searches all mail items, the archive content is included. Users or administrators can set retention policies so that mail is automatically moved to the archive after a number of days, and different policies can be set on different folders.

The goal of this feature is to kill off local PST files, which are a nightmare to maintain and backup and are very difficult to search and manage from a compliance perspective. Functions exist to allow delegation of search capabilities to compliance officers so they can easily find email over all mailboxes in the environment, and legal holds can be placed on items so they aren't deleted.

In my opinion, Microsoft has missed the boat on this feature. The fact that the archive has to be in the same mailbox database as the primary means that you can't host the primary mailbox on one tier of storage (such as higher availability, higher performance) and the archive on a lower tier of disk. The Microsoft position is that the lower tiered disk for the archive isn't required because all storage can now be just a bunch of disks (JBOD) because of the low IO profile of Exchange 2010. That being said, I think in a future Exchange service pack they will change this design to allow the archive to be in a separate mailbox database.

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