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DaggyStyle
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PostPosted: Sat Feb 06, 2016 7:54 pm    Post subject: usb 2.0 to gigabit Reply with quote

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
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PostPosted: Sat Feb 06, 2016 8:10 pm    Post subject: Reply with quote

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
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PostPosted: Sat Feb 06, 2016 8:18 pm    Post subject: Reply with quote

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.

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.


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.
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PostPosted: Sat Feb 06, 2016 9:03 pm    Post subject: Reply with quote

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
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PostPosted: Sat Feb 06, 2016 9:09 pm    Post subject: Reply with quote

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
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PostPosted: Sun Feb 07, 2016 2:13 am    Post subject: Reply with quote

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.
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PostPosted: Sun Feb 07, 2016 10:18 am    Post subject: Reply with quote

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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