Ask the Expert: Connecting two data centers
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Q: I'm connecting two data centers, 70km apart, and I want to use EMC Symmetrix for synchronous replication. Will that distance work?
A: Focusing on latency vs. bandwidth is a good start. Make sure you consider decibel loss, which is the amount of optical signal strength degradation over distance due to a weak light source, or light traveling over cable with many connections. Your bandwidth or optical carrier provider can tell you the actual distance and the decibel loss of the cable. Depending on the amount of data and how much it changes, it's possible you could do the synchronous replication. But check with EMC or dense wavelength division multiplexing suppliers (e.g., ADVA, Ciena and Nortel, among others) to get a better assessment. Make sure that what you're getting for bandwidth is actually a full lambda circuit and not some variation of a slower optical bandwidth service.
--Greg Schulz, founder and senior analyst, StorageIO Group
This was first published in June 2008