Transferring from a SSD to a hard drive(if you happen to have windows on it) can MAX out the hard drive and cause some interesting slow downs.
This should be almost unheard of on a secondary drive as well.
Transferring from one drive to another and overloading the disk in general, like with torrents, doesn't yield any slow downs. It's only using the network that renders it practically unusable until you cancel the transfer.
Resources won't show as maxed because it's not one particular program causing the lag. How many files are you sending at once that are that size?
It can be just one file of that size. I just sent a 3GB file and even that produced the same result.
What NIC are you using? This sounds like lag introduced by a NIC without interrupt moderation.
I'm using the on-board NIC from
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128510
I went in the device manager and checked on that function which it was enabled. I disabled it to notice a pretty decent speed increase on the file transfer.
Something interesting I noticed was having a list of large files on transfer from earlier was halted because there was another file with the same name . It had been sitting at that dialog for probably about 3 hours before I got back home and just pressed skip allowing the transfer to resume. When it resumed there was no latency until I started transferring a new file..
I should probably also mention that everything is fine when using other means to transfer things to networked devices like an FTP server.. only windows file sharing.