Archives for: March 2011

Bandwidth

05/03/11 | by admin [mail] | Categories: Hardware, Networking

Never underestimate the bandwidth of a station wagon full of tapes.
-- Dr. Warren Jackson, Director, UTCS

Many moons ago, on the original AmigaOne beta testers mail list, one of the mailers referred to their gigabit sneaker net. An external hard drive which they would walk home from the office with.

In networking terms, bandwidth is the capacity of the network to transfer data. If you ignore the underlying medium (which really doesn't matter), you can see that sneakernets often have very high bandwidth. Take a 3TB external drive. Over 10 mins (600s) the unidirectional bandwidth is 50 gigabit/s (assuming 10bits/byte). Of course, if you also need to transfer the data from a system to the 3TB drive, and then to another system, bandwidth is greatly reduced.

But back to the quote. Let's assume some 1.5TB LTO-5 tapes. Let's assume a rather conservative capacity of the station wagon of 5000 tapes. That's 7.5 petabytes. Over an hour, that would be about 16terabit/s, or Sydney to Melbourne about 1.5tbps. Which doesn't compare too badly to a fibre optic link.

Of course, sneakernets or stationwagon-nets may have high bandwidth, but there are two big issues to consider. One is that these nets are half duplex. If you require a network technology that allows you to communicate back and forth a lot, something involving time critical dynamic data processing (like gaming), it's not so great. The other thing to consider is transferring to transport medium from the system. Maybe with a hard drive, this is not such a problem. You could keep your home folder on an external hard drive or, maybe the whole system on a removable bay. But for tape, which is necessarily an offline medium, you lose a lot of time in the transfer.

However, if what you need to do a one transfer of a large amount of data, sneakernet or car net, will usually outperform ADSL, SHDSL or even 10mbit fibre.

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