High Bandwidth vs Low Latency?

Google FileSystem Paper -

High sustained bandwidth is more开发者_如何学Python important than low latency. Most of our target applications place a premium on processing data in bulk at a high rate, while few have stringent response time requirements for an individual read or write.

Wouldn't having a high sustained bandwidth automatically guarantee low latency?

Not necessarily. For example, an airplane filled with backup tapes flying from one side of the continent to the other has very high bandwidth because it gets all of the data there before any existing network could. However, it has very high latency because each individual piece of data took a very long time to get there.

Bandwidth is important when you have a lot of data to send/receive and it doesn't really need to be real-time, such as transferring large amounts of data to an off-site backup. (You don't really care in what order the data arrives or how quickly the other side can respond, you just need all the data to get there.)

Latency is important when timing is critical in how/when the data arrives, such as online gaming or video streaming. (You don't care how much data may have been dropped as long as the "current" packet is arriving "right now.")

Obligatory: "Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway." —Tanenbaum, Andrew S. (1996)

(The first Google hit on this quote was the Wikipedia page for Sneakernet, which is another excellent example of high bandwidth and high latency.)

(Or, in my case about a month ago, the bandwidth of a Scion carrying 2 TB hard drives down the highway. I transferred 15 TB of data in two days. Not bad for consumer-grade hardware.)