copy images from sd card to external hard drive

I copy my photos made with my camera from my SD card to my external hard drive using my MacBook pro retina 15". I have copied thousands of photos without any problems but since last week the copying is going really slow. I have to copy 150 photos and before that took about 5 minutes, but now there were only 4 photos copied after 3 hours of waiting.

How can I fix this or what can be the problem?

最后更新：2017-09-12 18:06:47