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Exchange 2010 and storage systems

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The latest version of Exchange Server has some significant changes that will impact the storage supporting the mail system.

By Brien M. Posey

With Exchange Server 2010, Microsoft Corp. made some major changes to the database structure that underlies the email application. These architectural changes have a significant impact on planning for Exchange Server's data storage requirements.

The biggest change Microsoft made was eliminating single-instance storage (SIS). Previously, if a message was sent to multiple recipients, only one copy of the message was stored within the mailbox database. User mailboxes received pointers to the message rather than a copy of the entire message.

The elimination of single-instance storage means that when a message is sent to multiple recipients, each recipient receives a full copy of the message. In terms of capacity planning, the overall impact of this change will vary depending on how many messages include attachments.

Text and HTML-based messages are typically small and will have a minimal impact on capacity planning, and Microsoft further reduces the impact by automatically compressing such messages. However, if you have users who routinely send large attachments to multiple recipients, those messages could have a major impact on database growth. Microsoft's primary goal in designing the new database architecture was to decrease database I/O requirements. As such, Microsoft chose

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not to compress message attachments because of the additional I/O that would have been required to compress/decompress them.

It may seem odd that at a time when storage managers are looking to reduce duplication in primary storage Microsoft removes a data reduction feature from Exchange. But Microsoft scrapped single-instance storage because Exchange mailbox databases perform much more efficiently without it. Microsoft claims database I/O requirements have been reduced by approximately 70% in Exchange 2010.

One of the most common methods of keeping Exchange 2010 mailbox databases from growing too large is to use mailbox quotas. Quotas prevent individual mailboxes from exceeding a predetermined size, and the quotas in Exchange 2010 work as they did in previous versions of Exchange with one notable exception. Exchange 2010 introduces the concept of archive mailboxes (discussed later). If a user has been given an archive mailbox, the mailbox quota won't count the archive mailbox's contents when determining how much storage the user is consuming. Exchange does, however, let you manage archive storage through a separate quota.

The use of mailbox quotas is a tried-and-true method for limiting data storage consumption. But Microsoft has been encouraging organizations to make use of low-cost storage rather than mailbox quotas. The argument is that organizations can accommodate the increased database size without spending a lot on expensive storage solutions.

The low-cost storage recommendation is based on more than just storage cost. Many organizations have been forced to set stringent mailbox quotas that have forced users to delete important messages. Ostensibly, cheaper storage will allow for larger mailbox quotas or for the elimination of quotas altogether.

This was first published in April 2011

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