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Replication alternatives

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Host-based replication

In host-based replication products, the replication software runs on servers so, unlike array- and network-based replication, it doesn't depend on additional hardware components. That makes host-based replication the least-expensive and easiest replication method to deploy.

"Deploying host-based replication only requires installing the replication software on source and target servers and you are ready to go," noted Bob Roudebush, director of solutions engineering at Double-Take Software Inc. It's well suited to work in heterogeneous environments, supporting the widest range of storage options that include both network- and direct-attached storage. While most products support Windows, Linux and Unix support is more tenuous and, therefore, platform support is clearly one of the critical evaluation criteria when selecting a host-based replication product.

On the downside, host-based replication adds processing overhead to servers and the installed replication software carries the risk of introducing unknown behavior. "For critical and high-end application servers, IT managers tend to favor array-based replication over host-based replication because it keeps server resources dedicated to the app and doesn't expose it to potential bugs or flaws in the replication software," said Lauren Whitehouse, an analyst at Milford, Mass.-based Enterprise Strategy Group. Furthermore, licensing costs and system administration duties

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increase proportionally with the number of servers, giving both array- and network-based replication an advantage in environments with a large number of servers. In addition, visibility in host-based replication is typically limited to source and target servers. This is very different from the centralized architectures of array- and network-based replication offerings that enable a more holistic view into the replication infrastructure.

The target markets for host-based replication products are typically small- to medium-sized businesses (SMBs) that can't afford more expensive replication alternatives, enabling them to deploy data protection and disaster recovery architectures that, until a few years ago, were only seen in larger firms. CA, Double-Take, InMage Systems Inc., Neverfail Inc. and SteelEye Technology Inc. are some of the vendors that have enabled smaller companies to deploy replication-based DR and data protection at a fraction of the cost of array- and network-based replication. Although each of these products replicates data from one location to another, they differ in features such as efficiency, bandwidth throttling, management, high-availability failover capabilities, platform support and application integration. Only a thorough product evaluation will reveal which product offers the best fit for a given environment.

In addition to these standalone offerings, backup software vendors are integrating host-based replication into their backup suites with the hope of expanding their reach into the lucrative remote- and branch-office data protection business.

"We see a convergence of DR and data protection, and consider replication to be a feature and not a standalone product," said Marty Ward, senior director, product marketing for the Data Protection Group at Symantec Corp. Most backup software vendors are already offering host-based data replication options for their backup suites; some examples include BakBone Software Inc.'s NetVault: Real-Time Data Protector; CommVault Continuous Data Replicator (CDR); EMC RepliStor to complement EMC NetWorker; Symantec Backup Exec Continuous Protection Server (CPS); and Symantec NetBackup PureDisk with a deduplication option, as both a standalone product and a NetBackup option.

The main advantage of combining traditional backups and replication is the ability to manage replicas and backups within a single tool. Aside from their host-based replication options, backup software vendors have been working on integrating their backup suites with leading storage arrays and network-based replication products to enable customers to manage all replicas and backups with the same tool.

This was first published in April 2009

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