# usb 2.0 to gigabit

## DaggyStyle

Greetings,

I need to speed up the network data transfer on my rpi2, I've thought of getting a usb to gigabit adapter like tp link's UE300.

I know that usb2.0 has a limit of 480mbps, question is, what actual speed I'll be able to get out from that device?

Thanks.

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## eccerr0r

Depends on your USB2, what have you seen with HDD's?

Also depends on the ethernet adapter. 

Really you won't know till you try, or someone else tries.

I've seen a good 35MB/sec through USB2 to a HDD, so I suspect a Gbit ether should also be able to get a good 35MB/sec or so over USB2 if it supports it.  Probably can get higher with USB3.

This is assuming your CPU can also handle it with the USB host adapter.

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## DaggyStyle

 *eccerr0r wrote:*   

> Depends on your USB2, what have you seen with HDD's?
> 
> Also depends on the ethernet adapter. 
> 
> Really you won't know till you try, or someone else tries.
> ...

 

rpi2's cpu is cortex a7 quad core at 900mhz.

why so low? max usb 2.0 is 480mbps=>60 MB/s. so lets reduce 10% we get 55 MB/s. so why should I expect 35 MB/s?

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## Ant P.

 *DaggyStyle wrote:*   

> max usb 2.0 is 480mbps=>60 MB/s. so lets reduce 10% we get 55 MB/s. so why should I expect 35 MB/s?

 

USB2 is PIO-only, no DMA.

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## DaggyStyle

 *Ant P. wrote:*   

>  *DaggyStyle wrote:*   max usb 2.0 is 480mbps=>60 MB/s. so lets reduce 10% we get 55 MB/s. so why should I expect 35 MB/s? 
> 
> USB2 is PIO-only, no DMA.

 in that case, what is the max possible transfer rate I can expect?

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## s4e8

 *DaggyStyle wrote:*   

>  *Ant P. wrote:*    *DaggyStyle wrote:*   max usb 2.0 is 480mbps=>60 MB/s. so lets reduce 10% we get 55 MB/s. so why should I expect 35 MB/s? 
> 
> USB2 is PIO-only, no DMA. in that case, what is the max possible transfer rate I can expect?

 

According to wikipedia, the effective throughput of USB2 is 280Mbit/s or 35MB/s

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## Ant P.

The main problem with PIO is that it's CPU-bound, and 900MHz is barely enough to run a USB stack + TCP/IP.

But the real performance-killer here is that Ethernet is full-duplex while USB 2 isn't (3 is), so you're basically stuck with 100Mbps each way.

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