Why is downloading over USB so slow?

Question

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

I was downloading a file from rapidshare.com 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?

Solution 1

It's a Firefox bug :-(

https://bugzilla.mozilla.org/show_bug.cgi?id=623866

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

Solution 2

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.

Comments

[David Schwartz]

What's the make and model of the flash drive? And what is "20 kb/s"? Is that kilobits per second?

[Honoki]

I meant to say kilobyte per second (kB/s). The flash drive is a HP v135w 8 GB key.

[ZEDA-NL]

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?

[Pablo Cacho]

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.

[Honoki]

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.

[LawrenceC]

Do you get this same speed when downloading a large file from sites other than rapidshare.com, and when downloading a large file using a different browser?

[Honoki]

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?

[David Schwartz]

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.

[Honoki]

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.

[mouviciel]

@Honoki - Have you tried with an external USB hard drive?

[Honoki]

No. See higher.

[Psycogeek]

What if the write cache was utalised more? what is the download chunk size and download type? open for write, write 1ks close re-open? I donno. But there are 2 settings in a windows system for USB flash to change how it caches or flushes or something, So called performance. If it is via a "locked down" system, mabey there is something drastically effecting that, or even a mess in the USB devices area from many many different flash chunks tossed on the same computer.

[Honoki]

That can't be the issue with this problem. See my comment on the first post

[Lèse majesté]

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.

[Honoki]

This was indeed on a Windows machine, if I recall correctly.