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I would like some advice on why this is happening to my USB devices...

I have tried a few USB 2.0 pendrives, FAT32, EXT4, NTFS. All no more than 16 GB big.

Read speeds are fine (25-27MB/s)

Write speeds however...

Start really fast i.e. 50 to 60 MB/s then drops significantly down to 10MB/s before gradually slowing down to 2MB/s and less.

Overall the copy process is extremely slow. 30min for 3 files totalling 4.5GB and even slower for 8,422 php/css/html files totalling 352MB.

Where do I begin? Google and forums yielded no help.

--Update--
I have run benchmarks since acquiring Windows 7 and various other flash pendrives and HDDs.

There is a significant difference. Windows shows transfer speeds averaging around 80MB/s where as Ubuntu never averages above 11MB/s. Same hardware, same USB ports.

This, along with poor battery life is quite disheartening.

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Try benchmarking on an SD card (in USB adapter), with Class -4, -6, and -10 type cards. See if this is write-speed, software, or bad (cheap) control chips in the USB devices you are using. –  david6 Nov 12 '12 at 9:39
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1 Answer 1

Write speeds are fast to begin with because the blocks of data are being cached and are in the process of being eventually written back to the slow device. After some time, the available memory for caching will run out and you then get throttled back to the speed of the underlying USB device. So this is why you see the performance drop over time for a large write to the USB device. So I expect you have a USB pendrive that has fast read access but slow writes, and the caching effect makes it seem that it fast to begin with but ultimately you are seeing the native write speed of your flash device.

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Yeah also noticed USB 2.0 can't go past 30MB/s. So speeds above that are due caching, as stated above. –  ThiagoPonte Dec 24 '12 at 13:02
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