I was having the same problem, USB Hard-Drive crashing all the time and having a severe performance issue.
I came across this post in another forum:
https://apple.stackexchange.com/questions/176148/external-hard-drive-deep-freezing-macs
Go to settings - Spotlight - Privacy(right tab) and add the drive in question.
The OS stop crashing but I am still having some performance issues and the drive still ejects once in a while, but less frequently.
luisinui
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