Tip: Keys to Keeping your Exchange Server 2010 Data Highly Available

Exchange Server 2010 offers a number of features to help you design a highly available (HA) solution that ensures the availability of most messaging services. Simply by deploy¬ing multiple Hub Transport, Edge Transport, and Client Access servers and placing the additional servers within the appropriate Active Directory sites, you can ensure availability of key messaging services if a primary Hub Transport, Edge Transport, or Client Access server fails.

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When it comes to Mailbox servers, you can use several techniques to improve availability and avoid having to restore from backups:

  • Database copies Each member server in a database availability group (DAG) can have one copy of a database that is hosted and active on another member server.Exchange uses continuous replication to create and maintain copies of databases.
  • Deleted item retention Deleted item retention allows users to restore a single item or an entire folder in Microsoft Office Outlook.
  • Deleted mailbox retention Deleted mailbox retention allows administra¬tors to restore deleted mailboxes without having to restore the mailboxes from backups.
  • Archive mailboxes Archive mailboxes are used to store users’ old mes¬sages, such as may be required to comply with company policy, government regulations, or legal requirements.
  • Retention policy Retention policy is applied to enforce message reten¬tion settings.When messages reach a retention limit, they are processed by Exchange based on the actions defined in retention tags that have been applied.This allows messages to be archived, deleted, or flagged for user attention.
  • Multiple mailbox databases By using multiple mailbox databases, con¬figuring storage appropriately, and distributing users across these databases, you can reduce significantly the impact of the loss of a single database and allow for faster restores when needed.

With all of these features in place and configured appropriately, you might not need traditional point-in-time backups of Mailbox servers or long-term data storage on tape.Keep the following in mind:

  • For high availability, it is recommended that you have at least three highly available database copies, which means one active copy and at least two highly available passive copies. A highly available copy is a copy that does not have a replay lag time and is not blocked for activation by an adminis¬trator. This means you’ll need at least three Mailbox servers in each highly available DAG.
  • For disaster recovery, I recommend having at least four database copies, which means one active copy, at least two highly available passive copies, and at least one lagged copy. A lagged copy is a copy that has a replay lag time. This means you’ll need at least four Mailbox servers in each DAG optimized for disaster recovery.

As part of your Exchange organization planning, you should have at least one Mailbox server in each Active Directory site. Because any database availability group can be extended to multiple sites, you don’t necessarily need to have multiple Mail¬box servers in each site, and having multiple site locations for Mailbox servers can help protect you against data center failures. For example, if Site A goes offline but Site B remains available, users who normally access their mailboxes in Site A would be redirected automatically to the appropriate Mailbox server in Site B, as long as you’ve configured your database copies appropriately.

To eliminate the need for point-in-time backups, you need at least two highly available copies in addition to the active copy. I also recommend having a lagged copy of a database. Having a lagged database copy can help safeguard against data corruption that is replicated to the databases in a group, resulting in a need to return to a previous point in time. Keep in mind that deleted item retention and hold policy are your first line of defense in case of accidental deletion of mailboxes and mailbox data.

If you have multiple copies of an active database, you’ll likely want one of these copies to have a long lag time. What is sufficiently long is subject to interpreta¬tion and the needs of your organization. Ideally, the lag time would be sufficient to allow someone to identify a problem and for an administrator to begin recovery. In a 24x7 environment, where administrators are always available, a sufficient lag time may be 12, 24, or 48 hours, depending on your needs. In other environments, a sufficient lag time likely would be measured in multiple days.

From the Microsoft Press book Microsoft Exchange Server 2010 Administrator’s Pocket Consultant by William R. Stanek.

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