HDD transfer speed over usb

E

exe163

[H]ard|Gawd
Joined
Nov 15, 2005
Messages
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I keep on wondering how come my hard drives have such a low transfer speed with USB. I have a MyBook and a USB docking station. Both of them cannot transfer past than 20MBs. When I switch back to sata, I get at least 3 times the transfer speed (more for my faster drives). Sata is faster than USB, I can understand that. But USB 2.0's rated transfer rate is 60MBs, what exactly is throttling the speed?
 
Overhead. USB is slow..

I've never gotten past maybe 25-30mb/s on USB.
 
And isn't the USB bandwidth shared ?

so if true, means anything that runs on usb would be slowing it down too?
 
USB is not efficient for large data transfert, lots of overhead. That is why at 480Mbps USB 2 is slower than Firewire is even if it's rated for 400Mbps. You will NEVER reach 60MB/s on USB 2.0 you will be lucky to get half that tops.
 
30mb/s tops for an external drive, but it drops quickly in my experience, 15-20mb/s is good
 
I am constantly connecting SATA drives to a USB 2.0 adaptor at work(server 2003) and I can get 40-50MBs all day long. I also get the same at home on my win 7 box.
 
strikerP4 said:
I am constantly connecting SATA drives to a USB 2.0 adaptor at work(server 2003) and I can get 40-50MBs all day long. I also get the same at home on my win 7 box.
Click to expand...

What SATA to USB controller do you use I wonder? Also, I have a R2E board, which has 6 USB on the back. How do I know which ports are shared among each other?
 
USB doesn't have DMA (direct memory access) transfers, unlike Firewire, meaning that all blocks of data have to be transferred by the CPU. This takes time and more effort, somewhat like PIO versus (U)DMA IDE. The USB protocol also adds a significant amount of overhead by itself.

eSATA > Firewire > USB.
 
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