Jaap de Vos (@[email protected])
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"Never underestimate the bandwidth of a station wagon full of tapes hurtling down the highway."
This quote about the bandwidth of physical transportation is roughly 10 years older than me. It came up in the Packet Pushers slack channel, and somebody wondered if it's still valid in 2025. Ouch! I got nerd sniped! Now I'm wondering too. Let's investigate.
To start, we'll need some numbers. This is gonna be pretty big on guesstimates, royally rounding things up or down, and ignoring some geometrical factors.
I can't ascertain the quote's origin, but I'm certain it originated in the USA. A 1975 American station wagon could have been a Ford LTD Wagon. Let's pick that one, it looks like a sweet ride. According to the brochure, it features a cargo volume of "over 100 cu. ft. counting lockable below-deck stowage". That's over 2,800,000 cubic centimers.
Let's choose a distance outside of the USA, UK, Liberia and Myanmar. That way we can stick with the International System of Units (SI), avoid dealing with miles, and avoid deteriorating our sanity any further.
One of my longer road trips featured a drive from Rome, IT to Dordrecht, NL: around 1600 kilometers. Assuming two alternating drivers, some bad traffic and some stops, let's say the drive takes us 25 hours.
The bandwidth could be 800 Gbit/s today, ignoring bandwidth-delay product. If you get creative with source and destination storage arrays and the network inbetween, you could conceivably multiplex and achieve some multiple, but 800 Gbit/s seems like a fair number so we'll stick with that.
Pushing 800 Gbit/s for 25 hours straight, we're are able to transfer a total of 9,000,000 gigabytes (9,000 terabytes or 9 petabytes). At this point I'm already intuiting the final answer, but let's move along.
According to a quick Google search, the highest capacity SSD for the last few years (HDD's don't come close anymore) has been the ExaDrive EDDCT100/EDDCS100 at 100TB. The ExaDrive is a 3.5" SSD. However, Solidigm is currently releasing a 122.88TB version of the D5-P5336 SSD. The D5-P5336 is a tall 2.5" SSD with a volume of 105 cubic centimeters. The weight is guesstimated at 300 grams.
A possible alternative are microSD cards. The highest capacity ones are 1.5 TB today. A microSD card weighs about 0.5 grams. The volume of a single card is about 0.165 cubic centimeters. So a microSD fits in the tall 2.5" SSD model roughly 636 times. Rounding up, the microSD's give us a nice single petabyte in the volume of a single tall 2.5" SSD, or almost a factor 10 difference. Interestingly, the weight of a single tall 2.5" SSD's volume is roughly equal to the weight of that same volume in microSD cards. So microSD cards it will be!
To keep things simple, let's work with the rounded numbers we have so far. 105 cubic centimeters worth of microSD cards will fit into the Ford LTD Wagon more than 25.000 times. However, that would be almost 10 million microSD cards, or almost 5000 kilograms of them. I can't find all the numbers for the Ford LTD Wagon, but the towing capacity I found was close to 1000 kg. I'm taking the towing capacity as an indication of the weight capacity of the car itself, even though there are different factors involved. Assuming a couple of humans and a bunch of stuff actually in the car during that towing, I'm picking a maximum of 1500 kg worth of microSD's. With two drivers, let's hope that the axles will hold and sacrifice a goat for zero speed bumps. 1500 kg would allow for 3 million microSD cards or 4500 petabytes.
One final note: we're ignoring the time it might take to transfer some data set from some storage array to 3 million microSD's (and to load them into the station wagon) before departing. We're also unsure about and ignoring any transfer time after arriving at the destination. I suspect these same assumptions were also in place about the tapes when the original quote was made.
The suggested drive will take 25 hours, and in that time the 800 Gbit/s connection will "only" transfer 9 petabytes. So with 4500 petabytes, the station wagon will transfer about 500 times more data than the 800 Gbit/s connection. Wow! You'd need a lot of multiplexing to offset the difference.
It's clear that the limiting factor is the weight capacity of the station wagon. A small truck or sturdy van would have been a more sensible choice. In any case, the station wagon wins hands down. Unless that old thing breaks down.
#bandwidth #storage #networking #stationwagon
