I have what appears to be the exact same problem. It has been working very well for ~2 weeks, but suddenly started being very slow.
It is almost as if disk access has slowed drastically.
I have tried:
- Actions-reset
- Reinstall Parallels
- Update windows system files (first step outlined here)
I'm running parallels 12 on Sierra
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You can delete this message if you like, but I think my issue was self-inflicted.
I had set up Crash Plan (running on Windows) to back up my VM as well and I think it was pulling in several of the items from the mac drive. At any rate, removing that seems to have fixed my issue. Definitely a corner case, but may help someone at some point.
Last edited: Dec 14, 2016