Farewell to Data Loss: Understanding Data Replication Page 3


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Finally, data-integrity and delivery must be highlighted when discussing asynchronous replication technology. To ensure the highest levels of data-integrity it is important to ensure the sequential transmission as well as the asynchronous replication of data. Given that asynchronous replication implies the potential of latency and it is possible to lose a packet across wide area networking, it is absolutely crucial to ensure that packets arrive at the target in the order that they were transmitted. The reason being that if an interruption were caused after only two blocks were written to physical disk, the source could recover from "A-B" (losing C), but the target data may be invalid if only "C-A" exists (losing B).

Nearly all replication technologies use standard networking protocols for delivery, with the one differentiator being whether they use a dedicated "cross-over cable" versus "standard-IP." Cross-over connections require that the servers be in relatively close proximity (same room or building), negating their viability for disaster recovery (DR). Using standard IP networking, in conjunction with the asynchronous replication, however, companies can deploy a cost-effective DR plan that transfers data without geographical limitations to an off-site location.

In conclusion, asynchronous replication technology allows companies of all sizes to cost-effectively protect a wide-array of data and applications, many of which were once left vulnerable due to financial resources and/or distance limitations. While synchronous replication technology is ideal for ATM or stock-related transactions, were "zero loss" regardless of price or performance is required.

Author Bio: David J. Demlow, vice president of product management, joined NSI in March 1997. He is responsible for defining the company's product roadmap and positioning. This includes identifying market opportunities and requirements from existing and potential customers, performing competitive analysis and monitoring overall industry trends and events. Demlow has more than 10 years of product marketing and management experience in the networking and storage industry.

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