A remarkably important (or remarkably silly, as the case may be) discussion has been going on for the past five years, beginning with a July 2006 post at Disruptive Library Technology Jester, continuing with comments on that post over three years, then recommencing with a June 2010 post at DLTJ and another June 2010 post right here.
All of these having to do with contemporary updates for the old internet adage, “Never underestimate the bandwidth of a station wagon full of tapes.”
I pondered the bandwidth of a 747 full of Blu-ray Discs (yes, Blu-ray Discs were around in 2006). Peter did some calculations, assuming the bulk of jewel boxes as the limiting factor. Over the years, this was refined and another person offered an Airbus A380 as an alternative factor. In every case, we concluded that the effective bandwidth for transcontinental data transmission of very large datasets was much higher on a 747 than on any known network–although latency was, and is, a bitch. (Still: If you want to ship 50 Terabytes of data from one place to another…well, you know, that’s only ten spindles of Blu-ray discs or, these days, 17 internal hard disks weighing about 30 pounds.)
As of last June, I concluded that weight was always the limiting factor–a 747 cargo freighter actually full of either hard disks or Blu-ray spindles couldn’t take off, as it would be way over its cargo weight limit–and that Blu-ray spindles won the actual bandwidth war, because 400 Blu-ray discs on four spindles (50 GB each, or 20 TB for the lot) weigh less than 10 two-terabyte hard disks (using Western Digital Black Caviar specs). In either case, the bandwidth was at least three orders of magnitude greater than the highest known network transmission bandwidth (160 Terabits/second as compared to 110 Gigabits/second).
Hard disks take the lead
Ah, but now the standard for everyday hard disks–ones produced by the millions at low, low prices by name-brand companies (specifically Western Digital) is 3 terabytes, not two terabytes.
And the Western Digital Green Caviar 3TB drive is a little lighter than the Black Caviar 2TB drive–0.73 Kg (1.61lb.) rather than 0.75 Kg (1.66lb.)
Net result: Using the full carrying capacity of a 748 freight configuration, which in this case is considerably less than 10% of its actual cargo volume, you could load a 747 with something like 169,390 WD 3TB drives, each holding 3TB or 24Tb (Terabits).
The net result: The effective bandwidth from New York to LA comes out to just over 250 Terabits/second–a little higher than the 232 Tb/s you can get with dual-layer Blu-Ray discs in 100-disc spindles. Either figure, to be sure, is more than 2,000 times the best internet bandwidth.
So what?
Mostly, this is for amusement. “Of course,” latency makes this meaningless–that is, the fact that the first byte transmitted arrives 16,200 seconds after it’s sent.
But is that always the determining factor? Let’s take a more modest real-world possibility:
You want to send me 60 historic movies at Blu-ray data quality–that is, 3TB worth of movies. You can send them to me over my DSL at an average 1.5Mb/s (that’s bits, not bytes). Which would you choose?
Hmm. 1.5MB/s = 187.5 kilobytes/second or 5.333 seconds per megabyte. Three TB = three million megabytes (this is disc capacity, so 1,000KB/MB, not the 1,024 you’d expect for RAM). Assuming no interruptions, entirely smooth performance, and nothing else using that line, it will take (calculate calculate) 185 days to send me the movies over the internet. Or, given that the hard disk weighs 1.6 pounds and fits in a 6x4x1.1″ package, you could ship it to me using USPS Flat Rate Small Box pricing, for $5.20; it would reach me two days later.
Sure, I could get faster broadband (no FIOS here), but I don’t think Comcast will let me stream three terabytes of data at anything like, say, 5MB/s guaranteed rate with no capacity caps or surcharges. If they did, well, that changes the picture: It would take a little less than two months (55.5 days) to send me the movies. Of course, if Comcast imposed a $5/GB surcharge once I passed the first 50GB, well…never mind that.
So, yes, there are real-world circumstances in which the net is the slow way.
Update on real-world example: If, say, the MPAA wanted to send 60 screeners to Oscar judges (thus, 3TB of data at Blu-ray resolution), they’d really use an external 3TB drive, costing a little more for postage and the drive…but still less than $170 total and 2-day shipping.
