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Why does downloading to flash memory over USB seem to be disastrously slower than to the hard drive?

I was downloading a file from using the Firefox addon DownThemAll. First I tried downloading directly to my USB flash drive over USB 2.0, which has a theoretical bandwidth of 480 Mbit/s, but the download got stuck at about 20 kb/s.

When I tried downloading the same file to a different location, /tmp on the hard drive, the download easily reached speeds of over 1MB/s.

How can you explain this difference if the bottleneck can't possibly be the USB 2.0 bus?

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What's the make and model of the flash drive? And what is "20 kb/s"? Is that kilobits per second? – David Schwartz Apr 18 '12 at 7:00
I meant to say kilobyte per second (kB/s). The flash drive is a HP v135w 8 GB key. – Honoki Apr 18 '12 at 7:05
Some computers have both USB 1.1 and 2.0 (or even 3.0) connectors. Could this be a problem? What OS are you talking about? – ZEDA-NL Apr 18 '12 at 7:11
You don't happen to have a usb hard drive lying around? If so, please check if the speed issue persists with that one too. – Jan Apr 18 '12 at 7:13
I'm on Ubuntu 10.04, but the connector can't be the problem (the transfer is very fast from HD to flash drive). I have no external hard drive to test with. – Honoki Apr 18 '12 at 7:17
up vote 5 down vote accepted

It's a Firefox bug :-(

It's been around for a while, but nobody cares enough to fix it.

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I would suggest the OP list the filesystem and OS he's using and check if this problem occurs with other browsers. If he's not using Windows, or if the flash drive is formatted using NTFS, then this bug should not affect him; likewise if it occurs with other browsers as well. – Lèse majesté May 2 '12 at 22:16
This was indeed on a Windows machine, if I recall correctly. – Honoki Jun 27 '13 at 23:03

USB flash drives are often very slow, pitifully slow. It's really that simple. It doesn't matter how fast the USB is if the flash is slow. The typical USB flash drive is an 8-lane superhighway that leads to a narrow alley.

I've actually seen USB flash drives that benchmark at 100KB/s. Though these days even the cheap ones typically hit 3MB/s.

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While I'm willing to believe this, I don't feel this can be all there is to it. How would you explain that when I later copy the file from /tmp to the flash drive, it easily reaches speeds of 8MB/s and more? – Honoki Apr 18 '12 at 7:07
Yeah, the v135w is actually a pretty fast drive, benchmarking around 8MB/s. So this isn't your issue. I wonder if it's something odd about DTA. – David Schwartz Apr 18 '12 at 7:10
Maybe the setting of my computer may have something to do with it. It's a computer connected to the intranet of my university. Logging in to it with my student details loads my personal files and settings over the network. Although I can't think how this could explain why the download speed is affected by the destination of the downloaded file. Maybe it is a DTA problem. – Honoki Apr 18 '12 at 7:15
@Honoki - Have you tried with an external USB hard drive? – mouviciel Apr 18 '12 at 7:32
No. See higher. – Honoki Apr 18 '12 at 7:44

The theoretical bandwidth limit of 480mbps for USB2.0 is simply the available bandwidth, not the actual speed devices perform at. The speed that USB devices perform at are based on the performance of the device itself. If you have a slower (read: CHEAPER) flash drive, it will run like garbage. If you properly research and find a flash drive with good performance, you will get that. Just like any device that is used for data transfer, it has speed ratings and speficifications.

Example: (Rated for UP TO 27MB/s write, UP TO 25MB/s read)

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That can't be the issue with this problem. See my comment on the first post – Honoki May 2 '12 at 21:55

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