Thank you Juan for your response. Without workers, (and by using the main process) the same issue occurs.
In response to potential issues with the hard drive. I have just checked the status of the harddrive and the read/write speeds. These seem to be fine. In addition, I have transferred about 1 TB of data from the hard drive a few days ago. I was able to do this at around 30 mb/s over long periods of time. So it don’t think it is a hardware issue.