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Troubleshooting, limit speed of USB3 device on USB2 computer.

Link to this post 21 Jan 12

Since the USB3 memory sticks are really fast I expect they would maximize the speed of the USB2 port (480Mbit/s). I tried two sticks. With Disk Utility I got a sustained read speed of 40Mbyte/s but when I tried the write I only got around 10Mbyte/s. During write the speed frequently went down to very low after starting at 35Mbyte/s. I tried several of the latest distros and the result were the same.

The plan was to try to set a hard limit on the speed to and from the USB3 device. I didnt find any such commands. Could I tunnel the USB traffic trough a simulated network device I then can traffic shape?

Link to this post 21 Jan 12

It looks like disk utility is a gui for hdparm and some other tools. have you attempted to use any of the common hard drive benchmarking software on the drive?

Link to this post 21 Jan 12

I think its accurate the result with file copy gets the same mean speed. Could you help me with usbnet driver under debian squeeze. I don’t know how to get usb0.

Link to this post 22 Jan 12

You need to understand that flash devices (thumb drives, SD cards, memory sticks) are MUCH faster at reading than writing. For SD cards, there are 10 classes of card (less actually, but they go from 1 to 10). The slowest you can get in the market is a class 2, and the fastest is a class 10. Most are class 6. The difference in write speeds is considerable. The difference in read speeds is not so much. So, just because a USB thumb drive is a USB 3.0 device and can read back data at 40MBps (320mbps) on a USB 2.0 port, it does NOT mean you can write at 320mbps on a USB 2.0, or even a USB 3.0, port at that speed! My experience is that 100mbps (12.5MBps) is about as fast as you are going to see. Isn't advertising/marketing great? :rolleyes:

Link to this post 22 Jan 12

If you look at the graph you see that write isnt stable. From 35MB/s down to 1 MB/s. What I would like to do is to limit the speed somehow to see at what speed it is stable.

Link to this post 22 Jan 12

Try the tests after:

sysctl vm.dirty_background_ratio = 10

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