Blackmagic test fast, file copy slow

Hello community! First post. Happy to be here.

I have an external USB 3.0 RAID-0 device that tests about 400MB/s read and write with Blackmagic Disk Speed Test, but file transfers using Path Finder and Finder average about 55MB/s.

This is a new thing happening with this device - wasn't always like this.

I was able to test it on 2 different iMacs, since I'm currently using the device to migrate to the newer machine.

-The volume is currently a Sierra boot volume (I used it to migrate my OS and accounts). Is that a possible cause?

-On the old machine (a mid-2011), I was using a Kanex Thunderbolt>USB3 adapter, and that one actually posted slightly higher write speeds - a little over 100MB/s. Way less than what I've seen in the past, but more than the new machine.

-On the new machine (late 2014), it's connected directly to a USB 3.0 port in the back. I haven't seen anything higher than 60MB/s.

I'd be eternally grateful if anybody had some experience with this and could shed some light.

Thanks!

G'day and welcomer to the forums.

Had similar problems. I use two external drives for backup, one Thunderbolt and one USB3. TB wrote to external drive at some 255Mb/ps anmd the USB3 at 55Mb/ps. The solution was the cable whilst claiming to be USB3 only worked at USB2 speeds. S new genuine cable fixed the problem. Appears there are tjhopusands of bogus cables out there, with many on auction sites.

Even had an 'Orico' look alike hub that fits to the front of my iMac to have USB3 ports available on the front of the iMac. Guess what? Yep USB2 also desite being sold as USB3.p


http://community.ebay.com/t5/Shippi...FAKE-USB-3-0-CABLES-BEING-SOLD/qaq-p/22018512

Hey harryb2448, thanks for your reply. Well, I never got to find out for sure what the issue was, because I ended up returning the new mac.

It turns out, once I formatted the RAID volume again (making it not boot media), the transfer speed returned to normal (at least on my old computer). I'm still not sure if it's related, but it's the best I can follow up with here.

Thanks again!