Currently Being ModeratedJan 1, 2013 12:53 PM (in response to BDAqua)
BDAqua is right. Transfer seepds are limited by the speed of the drive, so if you had an ssd in that could read/write around 400mb/s you'd get closer to the max speed of the USB 3.0, which is theorteically 5GB/s. I think.
Currently Being ModeratedJan 1, 2013 2:18 PM (in response to guino)
When I run a speed test w/ my G DRIVE 1TB external HD I'm only getting 60mb up and down. I see most people averaging 90-100.... I have a the brand new iMac w/ 3.1GHz i7 and 1TB fusion drive... Any ideas???
I think it is perfectly normal for newer 5400 RPM drives and even some older 7200RPM drives to have read-write speeds around 60-70MB/s, and USB 2.0 can reach 60MB/s--though rarely--so in addition to what others have said I'd also check to make sure that your drive is on a 3.0 SuperSpeed Bus and not a USB High-Speed bus (2.0). According to what I've read iMacs can USB 3.0 devices mounted on a 2.0 hub and a simple unmount, disconnect, reconnect will solve it. I know this has happened to me.
Select Apple->About this Mac->More Info...->System Report and highlight (click on) the USB entry at the end of the Hardware section. If your drive shows up as anything other than USB 3.0 SuperSpeed Bus then it is not running at USB 3.0 speeds.late-2012 27" i7 iMac, 32GB, 3TB Fu, OS X Mountain Lion, iPad '4'; ATV3; mid 2012 MBA;
Currently Being ModeratedJan 3, 2013 4:33 AM (in response to guino)
Odd quirk if you have the new 2012 iMac what you plug in first dictates the speed of that USB port, so if you plug in a USB 2 device that will dictate the speed of that port, you need to plug in USB 3 devices first to get maximum benefit, which seems really odd as far as I can see. Have a read http://support.apple.com/kb/HT5172
Currently Being ModeratedJan 3, 2013 4:49 PM (in response to killhippie)
Hey thanks for this bit of info but does it mean that if I first plugged in USB 2.0 into my ports that now my imac can only function at USB 2.0 speeds or is this on a reboot basis. Thanks!
Currently Being ModeratedJan 4, 2013 12:12 AM (in response to guino)
No problem, reading though the info it says
1) The first device you plug in will configure the port, so always connect USB 3 capable hubs or devices first.
2) What happens if if I plug in a USB 2 device into the USB 3 port first? If you plug in a USB 2 hub first, all devices connected or "daisy-chained" to that hub will operate up to the maximum transfer rate of USB 2 speed (480 Mbps)'
So I'm guessing once its done unless you either do a PRAM reset (just a guess) or go back to a point before you plugged the device in via time machine, but I would not like to hazard a guess it may mean a complete reinstall but that seems a bit ridiculous. I would plug in USB 3 first as it may be easier all round. Here is how to reset PRAM it may be worth a try if this does happen.