Is USB 3 a failure?

eSATA is better, but I've had mixed experience with it's reliability.

Maguscreed said:

That would be roughly a 60 megabyte/sec cap. That can't be accurate I've had sustained higher than that over 2.0.

I don't think that sounds right to me. 480megabits per second is correct...so 480,000,000 / 8 = 60,000,000 bytes per second / 1024 bytes = 58,593KB/sec. I've never seen a USB 2.0 device come close to 100% full saturation, about 70% with overhead is about as good as it will get. So, 60MB/sec x .70 = 42MB/sec is as fast as USB 2.0 is really going to go.

premier69 said:

i got som old 7200rpm drive in an old lacie usb2 external chassi and i get ALMOST 30mb/s.

That sounds a whole lot closer. I usually get 25-28MB/sec sustained transfer to my USB 2.0 devices.

...

so 480,000,000 / 8 = 60,000,000 bytes

That is not quite right. Although a byte has 8 data bits, there is also a 9th checkbit. Plus there is some checkdata that can be interleaved with the records. That's why I always quote a ratio 10:1 for bits:Bytes. That is not 100% right, but close enough and easy to convert.

The last image I took to a USB3 drive (5400 RPM disk), I got about 460Mb/sec write.

whs said:

The last image I took to a USB3 drive (5400 RPM disk), I got about 460Mb/sec write.

You got 460Mb/sec after the data was compressed and moved over to the external hard drive. Effectively, 460Mb of your system was backed up per second, but the actual throughput of the data to the device was slower. If you indeed got 460Mb/sec...you could have completed a 20GB image in just 40 seconds.

whs said:

...

so 480,000,000 / 8 = 60,000,000 bytes

That is not quite right. Although a byte has 8 data bits, there is also a 9th checkbit. Plus there is some checkdata that can be interleaved with the records. That's why I always quote a ratio 10:1 for bits:Bytes. That is not 100% right, but close enough and easy to convert.

Generally speaking though, when converting data transfer rates, you use 8 bits per byte as the accepted standard. You can see this website gets the exact same results that I came up with;
http://www.sengpielaudio.com/calculator-transferrate.htm.

Either way, with 8 bits or 10x...you are roughly the same amount of data...58-62MB/sec.

If you indeed got 460Mb/sec...you could have completed a 20GB image in just 40 seconds.

This you have to compute for me - but real slow please.

Here is my take:

460 Mb/sec is roughly 50MB/sec
20GB is 20,000 MB
20,000 divided by 50 is 400sec equal about 7 minutes

And that's about the time it took to take that image.

Btw: compressed or not compressed has nothing to do with it if the resulting image is 20GB - the amount of data in the partition was about 40GB.

sorry, I thought you were talking megabytes per second, but you indeed meant megabits per second. I screwed that one up. I usually try to refer to ###Mbps when I am talking megabits and ###MB/s when I mean megabytes. Totally my bad.

pparks1 said:

sorry, I thought you were talking megabytes per second, but you indeed meant megabits per second. I screwed that one up. I usually try to refer to ###Mbps when I am talking megabits and ###MB/s when I mean megabytes. Totally my bad.

Thanks, now I got my bearings back.