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.
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.
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
Neverfail is a true, automatic, active/passive fail-over solution. It uses primary and secondary Exchange servers linked via crossover cable to maintain a heartbeat connection and perform data synchronization. If the primary server experiences a hardware or software failure, the secondary server assumes its IP address and hostname and resumes operation. I tested Neverfail for Exchange 5.0. Neverfail Group offers a variety of application modules other than Exchange, including IBM Lotus Domino, Microsoft File Server, Oracle Database, SharePoint, and SQL Server.
Neverfail provides functionality comparable with that of Windows Clustering, and because it doesn’t require Windows Server 2003 Enterprise or DataCenter and Exchange Enterprise Edition, the overall cost is comparable. Neverfail goes beyond Windows Clustering in providing easier setup, great management, and an intelligent analysis and monitoring tool that can find and resolve problems on the Exchange server before they cause failures. Further, as opposed to Windows Clustering, Neverfail doesn’t require the hardware of the primary and secondary systems to be identical.
With the Neverfail system, LAN users don’t need to restart Outlook. The interval between failure of the primary server and starting the secondary server is short, about two minutes in my testing. Users connecting via MAPI or the Outlook Web Access client may need to restart the client to connect to the backup server.
The Neverfail system requires an additional NIC in the primary server, and a backup server running the same server OS and the same version of Exchange. Neverfail runs on Windows 2000 Server or Windows Server 2003, and it supports Exchange 2000 and Exchange 2003.
Setup is simple and straightforward. The Neverfail SCOPE (Server Check Optimization Performance Evaluation) utility identifies any performance or configuration issues with the Exchange server and recommends solutions before installing the fail-over software. It takes snapshots of server performance and performs trend analysis to identify areas that may become problems in the future. It also generates a system ID that Neverfail uses to create a license key. After the key has been received from Neverfail, the system clones the Exchange server to the backup system.
The installation copies all application files, registry settings, services, and data stores associated with Exchange, so the backup server is a perfect duplicate, including any software updates, service packs, and so on. The system monitors all the key services, as well as the main Exchange server process, so any problems -- even with associated software or performance degradation -- can trigger the fail-over.
Pricing begins at $7,600, which includes Heartbeat (the core engine), the Exchange module, and four SCOPE analysis cycles (the initial analysis of the server prior to installation, and three follow-up checks), as well as maintenance for one year. Pricing is per pair of servers, based on the server in the pair with the greater number of CPUs. A low-bandwidth module is available that enables compression and encryption over a WAN link, as well as asynchronous replication. This would normally be used for additional data backups rather than fail-over.
Neverfail is relatively expensive, especially if you have multiple Exchange servers. It is probably less expensive than using Microsoft Exchange clustering, and it’s much easier to set up. If you need 24/7 uptime for all e-mail users, Neverfail is a good way to go, although SteelEye’s LifeKeeper offers more functionality at a lower price.