Going the Distance for Disaster Recovery Page 2


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Complimentary New Technologies for DR

Complimentary new technologies for disaster recovery include native Fibre Channel over SONET, Fibre Channel over IP (FCIP) , and SAN Routing using the Internet Fibre Channel Protocol (iFCP). As a testimony to the commitment by customers to upgrade their disaster recovery plans, even established communications vendors such as Nortel are providing storage-specific solutions to accommodate Fibre Channel.

Similar to dark fiber/DWDM solutions, Fibre Channel over SONET and FCIP extend a single logical fabric over distance, but can drive much longer distances than dark fiber/DWDM links. SAN Routing with iFCP adds fault isolation and autonomous areas to DR scenarios, so that the production facility and DR site remain separate SANs and avoid exposure to potential fabric reconfigurations or state change broadcasts that affect extended fabrics.

Aside from technical concerns, there is also the very substantial issue of cost. IP wide area network services are more affordable than dedicated dark fiber and DWDM, but still impose a recurring monthly cost for what amounts to corporate data insurance. Customers today may select from a broad menu of IP service offerings, from link speeds as low as 1.54 Mbps (T1) to 2.5 Gbps (OC-48) with various service level agreements.

For storage traffic over IP, the recommended minimum bandwidth is 45 Mbps (T3), or roughly 5.6 MBps in storage vernacular. At full bandwidth saturation, a T3 link would carry about 700 MB per hour. While this may be more than adequate for many synchronous data replication applications, it has the added benefit of creating a wider backup window for remote tape streaming.

Driving More Storage Traffic over Longer Distances in Less Time

To facilitate use of lower cost and lower bandwidth IP links and still meet the requirements of storage transactions, vendors have created innovative technologies to drive more storage traffic over longer distances in less time. Data compression, for example, can more than double the payload delivery across a given link speed, enabling use of more affordable T3 services instead of OC-3 (155 Mbps) or higher links.

Algorithms such as Fast Write (originally developed by Nishan Systems and now provided by McDATA) can deliver a tenfold increase in payload delivery for Fibre Channel-originated data simply by eliminating most of the SCSI transaction overhead that would otherwise occur across distance. In addition, some bandwidth management techniques provide quality of service guarantees so that multiple storage applications can be run concurrently over the same IP infrastructure. These enhanced transport facilities optimize link utilization while providing more flexibility in choice for IP network services.

Interestingly, although European businesses have been in the vanguard of DR implementation, North American companies are breaking more distance barriers with DR. TELUS, for example, is a Canadian IP services provider that recently implemented a DR offering for its clients that spans between Toronto and Calgary, practically across the continent.

Global 1000 companies are now implementing much further reaching DR strategies, with links between Europe, North America and Asia. With new enabling IP storage technologies in hand, customers can focus on their enterprise-wide DR requirements and size their data availability strategies accordingly.

Tom Clark
Director, SAN Technology, McDATA Corporation
Author: Designing Storage Area Networks Second Edition (2003) (available at Amazon.com), IP SANs (2002) (also available at Amazon.com).

» See All Articles by Columnist Tom Clark

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