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Replication alternatives

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"Just like with Continuous Data Replicator, array-based replicas of supported arrays are integrated into the backup application index and catalog, allowing users to restore an array-based snapshot by simply right-clicking it within our application," said Brian Brockway, vice president of product management at CommVault. Similarly, Symantec's Veritas NetBackup is integrated with more than 40 arrays and virtual tape libraries (VTLs), and EMC NetWorker offers tight integration for EMC's RecoverPoint network-based replication product.

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Choosing a data replication solution

1. Selection of a data replication method should start with a business impact analysis to determine required recovery time objectives (RTOs) and recovery point objectives (RPOs).
2. For applications that can't accept data loss (RTO equals zero), synchronous replication is required. Heed latency in synchronous replication because it will drag down application I/O performance. If there is any risk of latency or unreliable bandwidth, or for replication beyond certain distances (50 km to 300 km), asynchronous replication is the way to go.
3. Besides the replication mode, application performance can be impacted by the replication platform. Host-based replication competes with applications for valuable processor, memory and I/O resources.
4. Have a clear understanding of the bandwidth requirements, impact on bandwidth cost, and how data replication will impact other applications and users. Clearly understand and take advantage of replication features related to bandwidth such as compression, bandwidth throttling and configurable bandwidth usage depending on the time of day. Consider wide-area network (WAN) optimization devices to preserve bandwidth.
5. Replication products that support heterogeneous environments can substantially reduce cost by supporting less-expensive or legacy arrays. They also limit vendor lock-in.
6. The disadvantage of vendor lock-in of array-based replication is offset by the advantage of close integration between replication and the storage platform and easier support, eliminating the risk of finger-pointing in multivendor configurations.

Network-based replication

In network-based replication, the replication occurs in the network between storage arrays and servers. I/Os are split in an inline appliance or in a Fibre Channel (FC) fabric; the I/O splitter looks at the destination address of an incoming write I/O and, if it's part of a replication volume, forwards a copy of the I/O to the replication target. Network-based replication combines the benefits of array-based and host-based replication. By offloading replication from servers and arrays, it can work across a large number of server platforms and storage arrays, making it ideal for highly heterogeneous environments. Most network-based replication products also offer storage virtualization as an option or as part of the core product.

This was first published in April 2009

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