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Vol. 2 No. 7 September 2003

Dense wavelength division multiplexing for disaster recovery

Dealing with distance Something to keep in mind as we delve deeper into this solution space is the distance in miles between the sites supporting your applications. The latency associated with the speed of light over an optical cable equates to a single data or management frame taking one millisecond per 100 miles. To address this latency, switch vendors recommend that you allocate more frame buffers at both endpoints of the long-distance storage area network (SAN) link. Increasing the frame buffers at both ends will allow the transmitting E_Port to have more frames in flight without waiting for an acknowledgment (ACK) from the receiving E_Port for having received previously sent frames. How many buffers should your E_Port support? Well, it depends on two things. For one, it depends on whether the application in question is synchronous or asynchronous in nature. The more synchronous, the more buffers you will need. It also depends on the speed and distance among connecting E_Ports. The greater the speed and distance, the more ...

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Features in this issue

  • Where tape belongs

    by  David Braue

    Ignore the industry babble about whether tape is dead or not: Tape is here to stay. But with the advantages of new low-cost disk systems--especially for fast restoration--tape's role in backup will likely change. The upshot: You'll likely be using your libraries differently.

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