Fail-over friends keep Exchange chugging

An e-mail server can stop delivering e-mail for several reasons: a loss of Internet connectivity, a hardware failure, an operating system crash, an e-mail server software crash, or a corruption of the database that stores the messages. The traditional backup-and-restore process can take hours to resurrect a server, and any mail that comes in while the server is down will be lost. As a result, not surprisingly, many organizations demand CDP (continuous data protection) for e-mail.

The options start with Microsoft’s own Windows Server 2003 Clustering Services and extend to a range of third-party fail-over and high-availability solutions. Windows clustering allows Exchange Server 2003 to be set up in either an active/passive cluster or a cluster of multiple servers with one standby server. This is highly effective in ensuring uptime, but it is complex to set up, requires extra hardware and licenses, and does not protect against data loss or database corruption (see “Windows clustering a costly option for Exchange fail-over”).

The solutions reviewed here can cope with almost any Exchange-related mishap, except Internet failures, and they do so more simply, at lower costs, and with additional flexibility or protection compared with the native Exchange cluster. Two solutions, Neverfail for Exchange and SteelEye LifeKeeper, bring true fail-over to an entire Exchange server. Two others, Cemaphore Systems MailShadow and Quest Availability Manager, protect individual mailboxes on one or more Exchange servers. And one, Lucid8 DigiVault, provides backup of data stores that can be restored to a secondary Exchange server. For maximum protection, administrators might choose to implement a fail-over system plus the CDP that DigiVault provides. (Yet another alternative is a high-availability Exchange appliance from Azaleos or Teneros. These solutions are installed on your premises but managed and monitored off-site. See our review "High-availability Exchange made easy").

Each product takes a different approach to protecting Exchange and offers different advantages. Some of the differentiators are, for example, whether an Exchange server license is required for the backup server, whether more than one server can be protected by a single backup server, whether an agent is required on each Exchange server, and whether replication over WAN links is supported.

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The test setup for each product consisted of a domain controller (Active Directory), two Exchange servers (the primary and secondary), and any additional servers as required by the individual product. I set up replication of the primary Exchange server to the secondary and then simulated failures by unplugging the network cable from the primary, stopping the Exchange Information Store service, and dismounting the drive the information store was running on, while monitoring incoming messages and simulating traffic using LoadSim. I observed the Outlook client experience when the primary server failed, as well as the time required to fail over to the secondary server.

Neverfail for Exchange