(rMBP 2015 15") Magic Mouse unusable during USB3 transfer
My Magic Mouse is practically unusable when there is any significant traffic on the USB bus. It just judders and lags terribly. It lags slightly when there is a drive plugged in, but if there is data transferring it is very bad indeed (currently transferring 130gb).
I bought this machine to replace my 2013 rMBP and never experienced the same issue. I frequently dump USB3 drives to my Thunderbolt RAID.
Machine specs:
10.10.4
rMBP 2015
2.5ghz i7
16gb Ram
512gb SSD
AMD Discreet graphics (I have graphics switching disabled and always have the machine plugged in)
Currently transferring from a USB3 WD 2.5" drive to my Akitio Thunderbolt array.
MacBook Pro with Retina display, Mac OS X (10.7.5)