Hot Spots: Step one for DR: Server virtualization


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Categories of replication strategies
Host-based replication solutions, such as CA XOsoft's Replication (formerly WANSync) or Double-Take Software's Double-Take, run on servers (or virtual machines in server virtualization environments) and asynchronously replicate data over an IP network from/to the disk arrays of choice. The challenge with this approach is that host-based agents may put an unnecessary load on the production systems the replication application protects, especially those in high transaction-intensive environments.

Network-based approaches, such as EMC's RecoverPoint or InMage Systems' DR-Scout, leverage a network-resident appliance or intelligent switches. The benefits are heterogeneous hosts and arrays (more flexibility and less vendor commitment), scalability and no performance impact on production systems. Disadvantages include the cost of the appliance or the investment in SAN fabrics that support embedded solutions.

Array-based products, including EMC's SRDF and Hitachi Data Systems' TrueCopy, reside on disk storage systems and replicate data between arrays without impacting host systems. Characterized as costly and array specific, array-based products don't allow source and target hardware to be mixed and matched.

Some replication products offer continuous data replication (CDR). These solutions maintain historical replication data--multiple,

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remote replica versions at a DR location. This capability protects against situations where a corruption is replicated and allows IT organizations to roll back to a known consistency point in time. Vendors offering CDR capabilities include CommVault and Double-Take.

Other replication products offer continuous data protection (CDP) as a feature. This capability captures data continuously, offering infinite points of recovery to a previous point in time. CDP also delivers more fine-grain recovery points than a CDR solution, as well as granular recovery of data (individual items, such as a message, mailbox or a database table). Replication vendors offering CDP capabilities include BakBone Software, CA XOsoft, EMC, FalconStor Software and InMage Systems.

When deciding on a strategy or vendor, remember that the goal of remote replication for DR is to mitigate risk. Preventing downtime, as well as responding to a disaster, is revolutionized with the introduction of server virtualization in DR environments. Server virtualization technology reduces the cost and complexity traditionally associated with remote replication for DR and DR testing, enabling companies of all sizes to introduce DR where it didn't exist before.

This was first published in April 2008

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