Exchange single-instance storage and its effect on stores when moving mailboxes

Single instance storage of message is the one of the most exclusive features of MS Exchange 5.5, 2000 and 2003 versions. When a message is copied and sent to multiple recipients and these recipients are located on the same database, the message is stored in Exchange server database only once. Exchange server then creates pointers, which link the original message to the original recipient and all other recipients. This feature of Exchange Server is known as single instance storage.

When all recipients including original and other recipients are moved to a new mailbox store, single copy of the message is kept in the new mailbox store.

Benefits of Single-Instance Storage

Following are some major benefits of single-instance storage:

• Single instance storage can reduce the quantity of archive media required since it avoids storing duplicate copies of the same message.
• With single instance storage, unnecessary space occupied by duplicate emails in backup media can be reduced, as only one copy of a file is written to it.

What happens when mailboxes are moved to an Exchange Server on another site?

In situations when mailboxes are moved to an Exchange Recovery Server on another site, pointers do stop functioning, as they become invalid. Process can become quite complex here, as each individual copy of the email has to be recreated and moved. In case of different mailbox stores a copy of message will be created for each store.

Exchange Server 2003 SP1 Move Mailbox Wizard

When there is a need to move Exchange mailboxes between stores, servers and administrative group, help of Exchange Server 2003 SP1 Mailbox Wizard can be taken to make entire process simple and easy. Its Cross Administrative Group Move feature maintains single-instance storage while moving Exchange Server mailboxes. In earlier versions of Exchange server this task is done through Exmerge tool but since this tool caused loss of single instance storage, it was not preferred much.

Once single instance storage is broken while moving from an Exchange Recovery server to another site, it cannot be recreated. Therefore being cautious while moving mailboxes is must to avoid problems.

Comments are closed.